Classification of Fishes: 8 Classes | Phylum Chordata

In this article we will discuss about the classification of fishes.

Class (1) Pterichthyes (Devonian) (Antiarchi):

The members of this class lived in the Devonian period. They are fresh water forms and the fossils that are well-preserved reveal certain internal structures.

(i) The head and the thoracic regions are provided with strong bony plates.

(ii) The arrangement of the bony plates is strikingly similar to that of the Class Arthrodira, but the mode of articula­tion of the head to the body is diffe­rent.

(iii) The tail is heterocerecal with a ventral fold.

(iv) The pelvic fins are usually absent.

(v) The intestine contains spiral valve.

(vi) A pair of large sac-like lungs is pre­sent.

(vii) The eyes are closely placed on the dorsal side of head.

(viii) The mouth is ventrally placed.

(ix) The jaws are poorly developed.

(x) The body is naked in some forms, but in Pterichthys the body and tail are covered with scales.

Order (1) Remigolepiformes (Upper Devonian):

(i) Pectoral appendages are not either jointed or subdivided into a proximal and distal part.

(ii) In between articular plates and termi­nal plate the area is covered with four longitudinal series of plates.

(iii) The posterior lateral plate is not fused with the posterior dorsolateral. e.g., Remigolepis.

Order (2) Asterolepiformes:

(i) Pectoral appendages are jointed and subdivided into a proximal and a distal part.

(ii) The distal part is covered with four longitudinal rows of plates.

(iii) The posterior lateral plate is united with the posterior dorsolateral plate, e.g., Pterichthys, Microbranchius, Bothriolepis (Fig. 6.51 A), Ceraspis.

Class (2) Coccostei (Arthrodira) (Up. Silurian – Up. Devonian) [Gk. Coccosteus, rough-like a berry bone;

Arthrodira, jointed double pieces]

(i) The members of this class are charac­terised by having strong cranial roof formed by the union of bony plates.

(ii) These bony plates are sculptured by the presence of tubercles.

(iii) The skull is articulated by a pair of condyles.

(iv) The vertebrae lack centra but the neu­ral and haemal arches are present.

(v) They are generally called ‘joint- necked’ fishes and flourished well during the Devonian period.

(vi) The posterior part of the body is pro­longed into a whip-like tail which may or may not be covered by scales.

(vii) An operculum covering the branchial arches is quite evident.

(viii) The pectoral fins are greatly reduced and are represented by a pair of small unmovable lobed structures situated one on each side of the body.

(ix) The pelvic fins are paired structures located on the ventral side.

(x) A well-formed dorsal fin is present.

The arthrodesis are fast-swimming and predatory forms. Some members of this group have attained large size. Dinichthys and Titanichthys have recorded to be about 9 metres in length. The actual systematic status of the group is controversial. Although they are claimed to be related to the dipnoans and elasmobranchs, their close relationship with the acanthodians is well-established.

Subclass (1) Euarthrodira [Gk. Eu, true; arthrodira, joined double pieces]

The head carapace usually possesses of four pairs of marginal plates, three median plates and a pair of central plates. The sensory canal system is open.

Order (1) Arctolepiformes (Acanthaspida) (Up. Silurian — Low. Devonian)

(i) The head is small and the body cara­pace is long

(ii) The paired fins are not found. Dermal skeleton is well developed. e.g., Acanthaspis

Order (2) Coccosteiformes

(i) The pectoral spine is immovable

(ii) The dermal skeleton is well deve­loped. e.g., Coccosteus (Fig. 6.51 B), Leptosteus, Oxyosteus.

Order (3) Ptyctodontiformes

(i) The dermal skeleton is ill-developed.

(ii) The pectoral fins are not found but a pair of pectoral spines are present.

(iii) The ventral fins are well-developed, e.g., Ptyctodus

Subclass (2) Phyllolepida [Gk. Phyllolepida, leaf scales]

(i) The dermal cranial roof is formed by one large median cephalic plate and five pairs of marginal plates.

(ii) The head and trunk armour are rigid­ly connected to each other, e.g., Phyllolepis.

Subclass (3) Macropetalichthyes (Anarthrodira) [Gk. macro, large, petalichthyes, flat­tened fishes; Gk. an, absent or without]

The members of this subclass have all the features common with the class Coccostei except the following points:

(i) The orientation of bony plates on the head is different.

(ii) The paired fins are constructed on different plan.

(iii) The ball-and-socket joint between the head and thorax is absent.

(iv) The pectoral girdle, pectoral fins and pelvic fins are cladoselachelike.

(v) The mouth is ventrally placed and the skull is dorsoventrally flattened-like elasmobranchs. This feature suggests their bottom-feeding habit. This sub­class presents many structural similari­ties with the elasmobranchs, acanthodes and many others. The exam­ples of the subclass are: Lunaspis, Macropetalichthys.

Appendix to Class Coccostei: Stegoselachii or Rhenanida:

Stensio (1936) united the several groups above the order rank under the term “Placoderm” (the plate skin). He included pterichthyes (Antiarchi), Coccostei (Arthrodira), Stegoselachii and Rhenanida. Other palaeon­tologists like Woodward (1932), Gross (1937), Romer (1946, 1966, 1971) and others have placed the above mentioned groups under the term placoderm.

But Berg (1940) expressed his opinion that the groups — Stensiochliformes (Stegoselachii) and Gemuendiniformes (Rhenanida) are insufficiently known and they are much more allied to coccostei rather than elasmobranchs, so these groups should be treated as appendix to coccostei.

Order Stensioelliformes (Stegoselachii):

The group is represented in Lower Devo­nian Coccosteans.

(i) The bead is armoured with bony plates and immovably remains attached with trunk.

(ii) The five gill openings are on each side and covered by operculum.

(iii) The pectoral fins are without spines and are much elasmobranch-like. e.g., Stensioella.

Order Gemuendiniformes (Rhenanida):

The group Gemuendiniformes (Rhena­nida) is represented by Lower Devonian Coccosteans.

(i) The body is flattened dorsoventrally resembling the modern rays, with a broad head. The mouth is situated at the anterior end.

(ii) The body is covered by small denti­cles which are attached to the bony plates.

(iii) The bony plates constitute the body armour.

(iv) The skull is fully ossified.

(v) The gills are covered by operculum.

(vi) The nasal openings are situated at the dorsal side in between the eyes, e.g., Gemuendina (Fig. 6.51 C), Asterosteus.

Order jagoriniformes:

The group is represented from upper Devonian period.

(i) The cranial roof is represented by iso­lated tubercles-like structure, not by plates.

(ii) The shoulder girdle is covered by der­mal bones.

(iii) The nasal openings are situated at the dorsal side, before the orbits.

(iv) The small, numerous teeth are not ankylosed with the jaws, e.g., Jagorina.

Class (3) Acanthodii (Upper Silurian to Devonian):

This class includes the most primitive pla­coderms. The members are smaller in size and are regarded as ‘needle-finned sharks’ because of their superficial resemblance with the shark. The acanthodians were fresh-water organisms and the geological history revealed their exis­tence from the upper Silurian to the Permian, their maximum abundancy being in the Devonian times.

(i) They had elongated fusiform bodies (almost eel-like) with a blunt snout.

(ii) The eyes were large and directed for­ward. The mouth was placed termi­nally.

(iii) The tail was heterocercal.

(iv) There were two dorsal fins in most cases, which may be reduced to one.

(v) A single anal fin was present.

(vi) Series of paired fins were present between the pectoral and pelvic fins. These were quite numerous in primi­tive forms and became reduced to none in subsequent stages. Each fin was supported by a large spine along with the anterior edge of the fin.

(vii) A well-formed pectoral girdle was present. Each half was composed of a scapula and coracoid which suppor­ted the spines of the respective fins.

(viii) Traces of basal elements were present in the pectoral fins.

(ix) The body was covered by small rhom­boid scales; The scales were dermal derivatives and were essentially com­posed of bony material.

(x) On the head region, the scales became enlarged and formed definite pattern of arrangement. The scales were comparable to the ganoid types.

(xi) The neurocranium, jaws and bran­chial arches were mostly cartilaginous in nature.

(xii) The jaws were primitive and had four ossified areas, two in the lower and two in the upper jaws.

(xiii) The upper jaw (palatoquadrate) was composed of two pieces and was toothless. The lower jaw was made up of mandible and possessed teeth.

(xiv) The teeth were modified scales.

(xv) The hyoid arch was an unmodified branchial arch.

(xvi) The mandibular, hyoidal and all the branchial arches in primitive forms, were provided with small opercular folds. But in the higher forms the mandibular operculum became high­ly developed to cover all the gills.

The acanthodians, as stated earlier, hold the ancestry of many, if not, all of the gnathostomes. On the basis of the work of Watson (1937), Berg (1940) created 7 orders and 9 families.

The orders and families are:

Order 1. Climatiiformes (Lowr Devonian):

Two dorsal fins and 3-5 pairs of spines are present between pectoral and ventral fins.

It includes 3 families:

(i) Climatidae, e.g., Climatius (Fig. 6.52A),

(ii) Euthacanthidae, e.g., Euthacanthus and

(iii) Parexicae, e.g., Parexus.

Order 2. Mesacanthiformes (Lower – Upper Devonian):

A single dorsal fin with a single pair inter­mediate spines between pectoral and ventral fins.

It includes single family — Mesacanthidae, e.g., Mesacanthus.

Order 3. Ischnacanthiformes (Upper Silurian):

Two dorsal fins but without spines in between pectoral and pelvic fins. Single fami­ly — Ischnacanthidae. e.g., Ischnacanthus.

Order 4. Gyracanthiformes (Lower Devonian — Carboniferous):

Large pectoral fins that reach to the last part of ventral fins. Single family — Gyracanthidae. e.g., Gyracanthus.

Order 5. Diplacanthiformes (Middle and Upper Devonian):

Two dorsal fins with a pair of spines in between pectoral and ventral fins. Single family— Diplacanthidae. e.g., Diplacanthus.

Order 6. Cheiracanthiformes (Devonian):

Single dorsal fin and without spines in between fins. Single family — Cheiracanthi- dae, e.g., Cheiracanthus.

Order 7. Acanthodiformes (Low. Carboni­ferous — Low. Permian):

Characters like dorsalfin and spines are as Cheiracanthiformes but without a coracoid. Single family — Acanthodidae, e.g., Acanthodes (Fig. 6.52B).

Remarks:

The systematic position of Acanthodii has been a controversial issue for a long time. Previously Acanthodii was included with the elasmobranchs. Watson (1937) considered the acanthodi­ans as most primitive gnathostome and ranked with the pisces. Romer (1962) included the Acanthodii with the Placodermii. Romer and Parsons (1986) consider that the Acanthodii is related to the ancestral Osteichthyes.

The acanthodians are considered to be the oldest known jawed vertebrates which appeared in the Lower Silurian. Bond (1996) and Kardong (2002) consider that Acanthodii is a class closely aligned with the bony fishes. Kent and Miller (1997) consider that acanthodians may have been the ances­tral jawed fishes.

Class (4) Elasmobranchii [Gk. Elasma = a flat plate; branchia = gills] (Plate-like gilled fishes) [Jurassic – Recent] Approx. 800 species:

The Class Elasmobranchii includes a group of fishes known as sharks and rays. The mem­bers of the class are also called elasmobranchs which literally signify the ‘plate-gilled’ fishes.

In spite of great morphological diversities, they form a very compact group, characterised by the following diagnostic features:

General features:

1. They are mostly of marine and predaceous forms.

2. The body is covered by tough skin con­taining minute dermal placoid scales (denticles) and mucous glands.

3. The mouth is ventrally placed. Rows of teeth (specialised placoid scales) are pre­sent in the mouth. The skeleton is cartilaginous in nature, but bone formation in the vertebrae has been recorded in small cat shark (Scyliorhinus canalicula).

4. The nostril may be one or two in number, but do not open into the mouth cavity.

5. The median and paired fins are present. The pelvic fins (in male) are provided with claspers. The fins are supported by fin-rays. The caudal fin is mostly heterocercal.

6. The notochord is persistent. The vertebrae are complete and separate.

7. The spiral valve is present in the intestine.

8. The swim-bladder is absent.

9. The heart possesses a contractile conus arteriosus with rows of valves.

10. The respiratory organs comprise of five to seven pairs of gills. Each gill is placed in a separate cleft. No operculum is present over the gills.

11. The opisthonephros is the functional kid­ney of adult fishes.

12. Jaw suspension is of hyostylic type.

13. Ampullae of lorenzini, an organ of sensi­tive electroreceptor, is present on the heads of sharks and on the pectoral fins of rays.

Fertilization:

14. The sexes are separate. The gonads are typically paired and the gonoducts open into the cloaca.

15. Fertilization is universally internal. The pelvic claspers of males with a solid skele­ton act as intromittent organ for copulation.

Development:

16. The eggs are large with massive amounts of yolk.

17. Elasmobranchs are either oviparous (Raja, Scyliorhinus) or mostly ovoviviparous. In oviparous species, the eggs contain much amount of yolk for nourishment and the eggs are often encased in a horny or lea­thery shell.

18. A specialized structure called nidamental gland, situated at the anterior part of the oviduct, secrets a proteinacaeous struc­ture that forms the horny or leathery egg shell. In ovoviviparous species the oviduct forms a uterus and many species are aplacental (cow sharks — Family Hexanchidae). The youngs of Mustelus and in other sharks form yolk sac placen­tae.

19. Cleavage is meroblastic, i.e., partial clea­vage.

20. Gestation periods are of two years, the longest period of any known vertebrate.

Chromosome Number:

The lowest diploid chromosome number (2n) for elasmobranchs is reported 14-24 in Scyllium canicula and the highest diploid number is 104 in Raja meerdervoortii.

Osmoregulation:

The marine elasmobranchs possess salt concentrations in the blood which are far below to the surrounding sea water. The osmotic pressure of the body is slightly higher (hyperosmotic) than that of sea water, due to the presence of high concentrations of urea and another organic compound — trim-ethylamine oxide(TMAO) which allow water to be drawn into the body.

Urea is the main nitrogenous end product of protein metabolism and gills are less per­meable to urea, so urea is reabsorbed by the large nephric tubules from the urine. Little water is drunk by the marine elas­mobranchs and some water enters through the gills, hence little amount of hyposmotic urine is formed. Excess urea is excreted by the kidneys and the gills. Excess salts are excreted by the rectal glands.

Thermoregulation:

Though the elasmobranchs (Sharks and rays) and rat fish (Chimaera) are ectothermic aquatic vertebrates, but in Lamnidae (Mackerel sharks — Carcharodon, Lamna and Isurus) are partially warm blooded and have modified circulatory system that enable them to retain a body temperature warmer than the surrounding water.

Classification with Characters:

The Class Elasmobranchii includes the sur­viving gnathostomes. Due to the lack of com­plete fossil records and intermediate stages, the subdivision of the class Elasmobranchii remains unsatisfactory.

However, all the elasmobranches can be divided into three subclasses:

1. Xenacanthii

2. Chadoselachiiand

3. Selachii.

Subclass (1) Xenacanthii (Pleuracanthodii):

The pleuracanthodians form a specialised group of fossil sharks which have been derived from the Devonian cladoselachians. They are fresh water forms. The fossils were abundant from late Devonian to Triassic period.

1. The body is slender with the dorsal fin extending along the body and tail.

2. The diphycercal tail has equally deve­loped blade of fin above and below the notochord.

3. The epichordal and hypochordal rays are equally developed.

4. The paired fins are paddle-like and are of ‘archipterygium’ pattern, i.e., having a long axis with pre- and post-axial rays.

5. A long spine is present on the head. The claspers are present.

6. The jaw suspension is amphistylic.

7. Five gill arches are present.

8. The two halves of pectoral girdle are sep­arated dorsally but fused ventrally.

9. The notochord is persistent.

10. There is no centra.

Order Xenacanthiformes (Low. Carboniferous – Low. Permian):

1. The mouth is about terminal.

2. The developed dorsal fin is separated from the caudal fin by a notch, e.g., Xenacanthus (= Pleuracanthus Fig. 6.52C).

Subclass (2) Cladoselachii (Pleuropterygii):

1. The body is elongated with terminal mouth.

2. There are two dorsal fins with broad base.

3. Anal fins are absent.

4. The caudal fin is hetrocercal internally but homocercal externally.

5. Fin rays are scarcely developed except caudal fin.

6. The notochord is persistent.

7. The jaws are amphistylic.

8. The teeth were cladodont, i.e., a principal median cusp and some smaller lateral cusps.

9. The males are without claspers.

Order (1) Cladoselachiformes (Up. Devonian – Low. Carboniferous):

1. There is no spines in dorsal fins.

2. The pectoral basalia is without a long seg­mented meta-pterygial axis, e.g., Cladoselache (Fig. 6.52D).

Order (2) Cladodontiformes:

The Pectoral basalia is with a long seg­mented metapterygial axis, e.g., Cladodus.

Subclass (3) Selachii (Euselachii) (Shark and Rays) (Jurassic – Recent) Approx. 763 species:

1. This group of sharks and rays have elon­gated or fusiform body.

2. Paired fins are without a median axis.

3. Base of pectoral fin is constricted.

4. Pectoral radials are jointed.

5. Tail is mostly heterocercal.

6. Males are with claspers.

7. Skull is either amphistylic or hyostylic.

Superorder (A) Selachoidei (Pleurotremata) Sharks [Gk. Pleuro = a rib or the side; tremata = opening):

(i) Body spindle shaped.

(ii) Tail heterocercal.

(iii) Gill-openings lateral and 5-7 pairs in number.

(iv) Anterior margin of pectoral fins free from the body.

(v) Right and left halves of pectoral girdle dorsally separated, not attached to the vertebral column.

It includes the fol­lowing orders:

Order (1) Hexanchiformes [Sixgills] (Mid. Jurassic – Recent):

A single spineless dorsal fin. Pectoral fins small to moderate in size. Caudal fin with a long dorsal lobe and the ventral lobe short. Anal fin present 6 or 7 pairs of gill slits on sides of head.

Family Chlamydoselachidae Garman, 1884 (Frilled sharks):

Body elongated and eel like. Mouth is nearly terminal. Cusped teeth in both jaws. 6- gill openings on each side of head. Anal fin larger than dorsal fin.

Examples:

Frilled shark, Chlamydoselachus anguineus (Fig. 6.53A) (Eastern Atlantic).

Family Hexanchidae Gray, 1857 (Cow sharks):

Stouter body, not eel like. Mouth sub-terminal. High, long cusped teeth in the upper jaw. Comb like teeth in the lower jaw. 7 pairs of gill slits. One dorsal fin.

Examples:

Sharpnose sevengill shark, Heptranchias perlo (Fig. 6.53B) (tropical and temperate seas recorded from south western India). Bluntnose six-gill shark, Hexanchus griseus (Fig. 6.53C) (Tropical and temperate seas).

Order (2) Heterodontiformes [Different teeth] (Up. Jurassic – Recent):

Two dorsal fins, each provided with a spine. Anal fin present. Five-gill openings. Two dorsal fins:

Family Heterodontidae gray, 1851 (Bull head sharks):

A spine on dorsal fin and an anal fin. Pig­-like snout, small anterior mouth. Rough skin and paddle-like paired fins. Enlarged first gill slits.

Examples:

Heterodontus (Indo-Pacific). Not recorded from the Indian water.

Crested bullhead shark, Heterodontus galeatus (Fig. 6.53D) (Western South Pacific).

Order (3) Lamniformes (Up. Jurassic – Recent) [Gk. Lammi = a voracious fish]:

Head conical to cylindrical and not late­rally expanded. 5 pairs of gill slits present on sides of head. 2 dorsal fins without spines.

Anal fin present. Spiracles usually present and very small. Jaws hyostylic.

Family Orectolobidae Gill, 1896 (Cat sharks and Whale sharks):

Long tails:

Dorsal fins equal-sized. Dorsolateral small eyes without nictitating membranes. Narrow dermal flaps along the side of the head.

Marine, worldwide. 13 genera (ParascyIlium, Cirrhoscyllium, Brachaelurus, Hetero- scyllium, Orectolobus, Chiloscyllium, Hemi- syllium, Stegostoma, Ginglymostoma, Nebrius, Rhiniodon etc.) with 33 species.

Examples:

Bamboo shark, Chiloscyllium (tropical waters); Zebra shark, Stegostoma (Indo-west Pacific); Whale shark, Rhiniodon (= Rhineodon) (tropical and warm temperate seas); Wobbegongs, Orectobus (Western Pacific).

Indian Species:

Slender bamboo shark, Chiloscyllium indicum (gulf of Mannar, Digha coast of W. Bengal); Grey bamboo shark, C. griseum (Fig. 6.53E, F) (east and west coasts of Indian peninsula); Zebra or tiger shark, Stegostoma fasciatum (recently in use Stegostoma tigrinum (Fig. 6.54A, B) (Indian coasts, mainly gulf of Mannar); Whale shark, Rhiniodon typus Smith, 1828 (common in Gujarat and Bombay coasts). The whale shark is the largest fish which is 60’9″ in length and 90,000 lbs in weight, was caught in the Gulf of Siam in 1919.

Remarks:

There is a considerable variation in the spelling of the generic name of the whale shark. Various spellings are Rhinodon Smith, 1829; Rhinchodon Smith, 1829; Rhinodon Muller and Henle, 1839. Of the following names, Rhineodon typus Smith 1829 is also used at present.

Family Lamnidae Muller and Henle, 1838 (Mackerel sharks, white sharks):

Large sharks with pointed snouts and spindle-shaped bodies. Large, blade-like teeth. Long gill slits. Long pectoral fins. Large first dorsal fin. Small 2nd dorsal and anal fins. Keeled and precaudal pits on the caudal peduncle. Lunate caudal fin. Marine, worldwide, tropical, sub-tropical and cold-temperate waters. 5 genera (Alopias, Cetorhinus, Carcharodon, Lamna, isurus) with 9 species.

Examples:

Thresher sharks, Alopias (Fig. 6.54C) (Circumtropical); Basking sharks, Cetorhinus (Amphitemperate); Great white shark, Carcharodon (mostly amphitemperate).

Indian species:

Great white shark, Carcharodon carcharias (Fig. 6.54D); Big nose shark, Carcharhinus altimus (South-eastern India); Black tip shark, C. limbatus (Indian coasts); Spot tail shark, C. sorrah (Western and south-eastern India).

Family Carcharhinidae Jordan and Evermann, 1896 (Grey sharks):

Small to large, elongated sharks with round eyes and depressed body. Usually no spiracles and blade-like teeth in both jaws. 2 dorsal fins, first dorsal fin moderately large and well ahead of pelvic bases. The second dorsal fin is much smaller than the first. Caudal fin with a strong ventral caudal lobe.

Marine, warm and temperate seas; a few members of this family may enter and live in fresh waters. 12 genera (Carcharhinus, Scoliodon, Galeocerdo, Glyphis, Isoqomphodon, Lamiopsis, Loxodon, Nasolamia, Negaprion, Prionace, Rhizoprionodon, Triaenodon) with 48 species.

Examples:

Ganges shark, Glyphis (Carcharhinus) gangeticus (Ganges and Hooghly river). Spadenose shark, Scoliodon laticaudus Muller and Henle, 1838 (= Carcharias sorrakowah Cuvier, 1817) (= Scoliodon palasorra (Bleeker, 1853) – com­mon throughout the Indian coasts.

Remarks:

Scoliodon laticaudus Muller and Henle, 1838, reassigned as Carcharias (Scoliodon) lati­caudus Muller and Henle, 1839 as holotype.

Family Sphyrnidae Gill, 1872 (Hammerhead Sharks):

Head flattened in front and expanded as a hammer.

Marine, tropical and temperate seas. 2 genera (Sphyrna and Eusphyra) with 9 species.

Indian examples:

Eusphyra blochii (Bay of Bengal, West Indian Coast); Scalloped ham­merhead, Sphyrna. lewini (Indian coasts); Great hammerhead, S. mokarran (Coasts of India); Smooth hammerhead, S. Zygaena (Gulf of Mannar, Kerala coast).

Order (4) Squaliformes (Up. Cretaceous – Recent):

Cylindrical or compressed body. 5 gill slits. 2 dorsal fins provided with spines or without spines. No anal fins. Usually spiracles present and well behind or close behind eyes. Jaws hyostylic.

Family Squalidae Blainville, 1816 (Dogfish sharks):

Short nosed cylindrical sharks. First dorsal fin is in front of the basis of pelvic fins.

Examples:

Ornate dogfish, Centroscyllium ornatum (Bay of Bengal, Arabian sea); Short spine spur dog (Squalus mitsukurii Jordon and Snyder, 1903 (Fig. 6.55A) (= S. acanthias Linnaeus, 1758 = S. fernendinus Molina, 1782) (Western North Pacific, Western Indian ocean). Other genera are Deania, Centrophorus, Scymnodon, Squaliolus, Scymnodon, Etmopterus.

Family Pristiophoridae Bleeker, 1859 (Saw sharks):

5 or 6 pairs of gill openings. Head some­what depressed. Much elongated, flat saw-like snout with a pair of ventral barbels. Spineless two dorsal fins.

Marine:

2 genera and 5 species-.

Examples:

Pliotrema with a single species (P. warreni) found mainly in the south-east coastal region of S. Africa at depths of 60-120 m. Pristiophorus, (Fig. 6.55B); with 4 species; mainly found in the coasts of Australia, Japan, Cuba, Bahamas and Florida.

Family Squatinidae Bonaparte, 1838 (Sand devils, Angel sharks):

Batoid-like forms:

Free anterior pectoral lobes. Enlarged hypochordal lobe of the cau­dal fin.

Marine, Indo-pacific and Atlantic. Single genus and 12 species.

Examples:

Squatina (e.g. 5. californica, Fig. 6.55C) (found in eastern Atlantic, western North and South Atlantic, Indian Ocean mainly around Australia, and North and South Pacific).

Superorder (B) Batoidei (Hypotremata) Skates and Rays. (Up. Jura. – Recent) [Gk. Hypo = below]:

(i) Depressed body.

(ii) Gill openings ventrally placed.

(iii) Anterior margin of pectoral fin is fused with sides of body or head.

(iv) Dorsal fins, if present, placed far behind.

(v) No anal fin.

(vi) They spend much time on the bottom and are mollusc-eating fishes.

(vii) Presence of a larg spiracle behind the eyes.

Order (5) Rajiformes (Up. Jurassic – Recent):

No electric organs between head and pec­toral fins.

Family Rhinobatidae. Muller and Henle, 1838 (Guitar Fishes):

Depressed body and tapering snout. Elongated caudal region and large spiracles. Well expanded pectoral fins. Dorsal fins with spines.

Marine, Tropical and Subtropical seas. 7 genera Aptochotrema, Platyrhina, Platyrhi- noidis, Rinobatos, Zanobatos, Zapteryx etc. with about 52 species. In India 4 genera with 10 species have been recorded.

Examples:

Rhinobatos (Rhinobatus) granu­lans, Fig. 6.56A (common in Indian coasts).

Family Pristidae Bonaparte, 1838 (Saw fish):

Anterior part of the nostril is more elon­gated and serrated, appears like a saw.

Marine, Indo-pacific and Atlantic. 9 genera with about 200 species. In India 3 genera (Raja, Breviraja and Cruriraja) have been recorded.

Indian species:

Pristis, Fig. 6.47B; Pristis cuspidatus (Coromandal coast); P. microdon (Bay of Bengal, Western Indian Coast).

Family Rajidae Bonaparte, 1831 (Skates):

Disc broad and rhombic formed by pec­toral fins. Usually two dorsal fins on the tail. Caudal fin rudimentary. Males with a series of spinous hooks on upper side of the pectoral fin.

Marine, Indo-Pacific and Atlantic. 9 genera with about 200 species. In India 3 genera (Raja, Breviraja and Cruriraja) have been recorded.

Examples:

Raja mamillidus (Bay of Bengal). R. reversa (Bay of Bengal).

Family Dasyatidae (= Trygonidae) Jordon, 1888 (Sting Rays):

Disc sub-rhombic broader than long and pectoral fins confluent with the sides of head Dorsal fins absent. Tail whiplike.

Marine, Indo-Pacific and Atlantic Oceans. 9 genera with 85 species. The genera-are Dasyatis (= Trygon), Himantura, Hypolophus, Urogymnus, Poratrygon etc.

Indian examples:

Dasyatis (= Trygon) sephen (cow tail ray); Trygon zygei (Paleedged sting ray, Fig. 6.56B); Dasyatis uarnak, (Banded whip tail sting ray); all common in both coasts of India.

Family Myliobatidae Bonaparte, 1838 (Eagle rays):

Disc much broader than long. Tail whip like with a single dorsal fin at the base.

Marine, Indo-Pacific and Atlantic Oceans. 5 genera (Aetobatus, Aetomylaeus, Myliobatis, Pteromylaeus and Rhinoptera) with 29 species. In India 3 genera with 5 species are recorded.

Indian example:

Aetomylaeus (Aetomylus) nichofii (Neuhof’s eagle ray, Fig. 6.56C), com­mon in both coasts. Spotted eagle ray, Aeto­batus flagellum occurs in S. India, and in Chilka lake; Javanese cow ray, Rhinoptera javanica occurs in west and south coasts.

Family Mobulidae (Manta rays, Devil rays):

Head distinct from disc with a prominent snout. Horn-like cephalic flippers. The fins are expanded in front of head which are used to collect food.

Marine, Tropical seas. 2 genera with 10 species.

Examples:

Manta (Manta rays) and Mobula (Sea devils). In India 2 genera with 3 species are recorded. Manta birostris (Fig. 6.57) grows over 7 m and is recorded in the gulf of Mannar.

Order (6) Torpediniformes (Electric Rays):

An electric organ on each side of the head, between head and pectoral fin.

Family Torpedinidae Bonaparte, 1838 (Electric Rays):

Disc sub-circular in shape. Two dorsal fins and a spineless caudal fin. Skin smooth. Marine; Indo-Pacific and Atlantic Oceans. 10 genera (Torpedo (Fig. 6.56D) and Hypnos sub-nigrum, [monotypic, Australian coasts], Narcine, Narke, Hetronarke, Astrape etc.) with 39 species. In India 6 genera with 14 species have been recorded.

Indian species:

Brown electric ray, Torpedo marmorata, Narcine brunnea; Spotted electric ray, Narcine indica (= N. timlei) (Fig. 6.56E); Numb fish, Narke (Astrape) dipterygia (Madras coast, estuaries of W. Bengal and Orissa). T. marmorata is common in the gulf of Mannar. N. brunnea occurs along the west coast and ranges east coast up to Hooghly. N. indica is common in the Gulf of Mannar, around Kanya Kumari and along the Gujarat coast.

Class (5) Holocephali (= Bradyodonti) (UP. Devonian — Recent) [Gk. Holos = whole; kephale = head].

Lund (1977) used the term Bradyodonti instead of Holocephali. Approx. 30 living species.

General features:

1. Body is somewhat compressed and naked in adult.

2. 5-gill arches are present. No spiracles.

3. 4-gill openings are protected by a single fleshy gill cover.

4. Bony plates are on the jaws instead of teeth used in crushing.

5. Cloaca is absent.

6. Skull is holostylic (palatoquadrate is often fused to cranium).

7. No bone in the skeleton (cartilaginous).

8. No bony fin rays and no bony plate scales.

9. Pectoral fins broad and leaf-shaped.

10. The upper jaw cartilage, palatoquadrate is fused with neurocranium (the base of cra­nium), a character which indicates the name (holos = whole; cephalos = head).

11. Diphycercal caudal fin.

12. Two dorsal fins, the first with a spine.

13. Extra claspers of unknown function on the head of males, and are called cephalic claspers.

14. Tail slender and whip-like.

Development:

15. Oviparous. The chimaeras lay their eggs in spindle or bottle-shaped egg cases.

16. Cleavage holoblastrc.

Geographical distribution:

They occur in deep seas. They are found in all oceans, from arctic and subarctic waters to the tropics.

The extinct numbers of the class are Squatoraja and Myriacanthus.

Subclass Chimaerae:

Pectoral fins of a normal type. Notochord persistent, usually en-sheathed by calcified rings. No true centra.

Order Chimaeriformes [30 species]:

Family (1) Chimaeridae (Short nose chimeras):

Examples:

Chimaera monstrosa (Fig. 6.58A), also called Rat Fish or “king of Herrings”, is found off the coasts of Europe, Japan, Australia, New Zealand, the West coast of North America and off the Cape of Good Hope. Another species are C. Affinis (Portugal coast); C. (Hydrolagus) colliei (North Pacific, specially South Eastern Alaska).

Family (2) Callorhinchidae (Elephant fishes):

Snout with a hoe-shaped terminal lobe; heterocercal caudal fin.

Examples:

Callorhynchus (Callorhinchus) antarcticus (Fig. 6.58B); C. capensis (Cape of Good Hope).

Family (3) Rhinochimaeridae (Longnose chi­maeras):

Snout is elongated and pointed.

Examples:

Hariotta raleighana (Fig. 6.58C) — occurs in Atlantic. Rhino-chimaera atlantica (Atlantic ocean).

Remark:

Holocephali shows many remarkable resemblances with the ptycodontid placoderms and may be considered a related group to them (Bond, 1996).

Class (6) Dipnoi (Dipneusta) [Middle Devo­nian — Recent] [Gk. Di = double; pnoi = breath] [6 living species]:

The Dipnoans or lung-fishes constitute this class. The position of the dipnoans amongst the fishes is quite significant. They constitute a sort of transitional group between the teleostei and the amphibians.

General features:

1. External gill opening single and covered with a bony gill cover.

2. Paired fins lobate, with a jointed median axis.

3. Peculiar grinding teeth usually present on the palatal regions.

4. Absence of articulated tooth-bearing pre- maxillary and maxillary bones.

5. Presence of internal nares that open into the mouth.

6. Air bladder serving as a lung with special pulmonary circulation.

7. A cloaca is present.

8. Autostylic skull (palatoquadrate is fused to the undivided cranium).

9. Median fins are fused around the posteri­or third of the body.

10. Braincase and vertebral column are poor­ly ossified.

Fertilization:

11. Fertilization is external, following a com­plex courtship.

12. Oviparous and the dipnoans lay their adhesive eggs on the selective vege­tation.

13. Parental care has not been observed.

Development:

14. Eggs are jelly-coated and are about 3 mm in diameter.

15. Cleavage holoblastic.

16. Yolk plug formation takes place during the gastrulation.

17. Development is indirect, i.e., with a larval stage having external gills, (e.g., Protopterus and Lepidosiron).

Chromosome number:

The diploid number in Neoceratodus forsteri varies from 32 to 38, in Lepidosiren paradoxa 38, 36, 38 and in Protopterus annectans is 34.

Physiology:

Osmoregulation:

The dipnoans are fresh­water animals; so they excrete mostly ammo­nia through the gills. The aestivating dipnoans (Protopterus sp.) when spend in the cocoons of the dried mud, converts urea from waste nitro­gen which stores in the blood and concentra­tions may reach as high as 3%.

Superorder Ceratodi (Lower Triassic — Recent):

Caudal fin is diphycercal, confluent with dorsal and anal. No gular plates. Cranial roof bones are few but large.

Order (1) Ceratodiformes:

Air bladder unpaired. Lateral rays of the paired fins well developed. The typical repre­sentative is Neoceratodus forsteri (Australia). The Mesozoic form, Ceratodus is included under this order.

Order (2) Lepidosireniformes:

Air bladder double. Lateral rays of the paired fins extremely reduced. Examples: Protopterus (Africa), Lepidosiren paradoxa Fitzinger, 1836 (South America).

Class (7) Teleostomi (Lower Devonian — Recent), About 20,994 living species:

The representatives of the class constitute the highly developed forms amongst the fishes. They possess many diagnostic features which separate them from other classes of fishes. Des­pite the wide ranging of the adaptive features, they possess the following common features.

General features:

1. The body is covered with thin dermal cycloid, ctenoid or ganoid scales and many lack scales entirely, e.g., the mem­bers of the family Siluriidae and some bottom dwellers.

2. The unpaired and paired fins are mostly present. The fins are supported by bony fin-rays. The tail is homocercal.

3. The mouth is terminal and is provided with teeth.

4. A single external gill-opening is covered by a bony operculum.

5. The jaw suspension is usually hyostylic.

6. Generally vertebrae are amphicoelous type.

7. Usually cloaca is absent.

8. An air bladder is usually present, some­times acts as lung in some forms.

9. The heart is two chambered (one auricle and one ventricle) with sinus venosus and conus arteriorsus.

10. Forebrain is feebly developed.

Fertilization:

11. Sexes are either unisexual or herma­phrodite. Hermaphroditism is widespread in Sparidae, Scaridae, Labridae, Pomacentridae and Muraenidae. Hermaphroditism may be recorded in Indian salmon, Eleutheronema tetradactylum.

12. Fertilization is external in most of the members except in some members of the two orders Cyprinodontiformes and Perciformes where internal fertilization is observed.

13. Oviparous or some members are viviparous where internal fertilization takes place (e.g., Cambusia, Poecilia, Sebastes norvegicus, Zoarces viviparus and Latimeria chalumnae).

14. Some members of marine fishes and most of the freshwater fishes lay adhesive eggs on aquatic vegetation, rocks, sands and gravels, and single or both sexes of the parents guard the eggs and youngs.

15. Formation of nests and parental care are seen in many species.

16. The eggs of some forms are carried in the- mouth, on the fins, under lips or skin grooves.

Development:

17. Eggs with large amounts of yolk – macrolecithal.

18. Cleavage is meroblastic, i.e. partial.

Chromosome number:

The diploid chromosome number of teleostean fishes has reported 12 in Conostoma bathyphylum (lowest diploid number) and more than 400 in Diptychus dipogon, a member of Cypriniformes. Most species have 2n number between 40 and 80 with a median of about 60.

Remarks:

The three classes, the Acanthodi, Sarcoptrygii and Actinopterygii, are thought to form a monophyletic group, termed the Teleostomi.

The class Teleostomi is divided into two subclasses: (i) Crossopterygii (Lobe fin fishes) and (ii) Actinopterygii (Ray fin fishes).

Subclass (1) Crossopterygii (Lower Devonian — Recent) [Gk. krossoi = fringe; pterygion = fin] (2 living species):

The crossopterygians represent a very interesting group of fishes and possess many characteristics of the tetrapods.

The crossop­terygians possess the following features:

1. The paired fins are provided with a large median lobe and are covered by scales.

2. The pectoral fins are supported by a join­ted median axis bearing radials on each side.

3. Scales are covered by a thick cosmine layer.

4. Two dorsal fins are present.

5. A pair of large gular plates are present.

6. Many ancient members had inemal nares but living forms do not possess any choana.

7. Caudal fin heterocercal, diphycercal or hetero-diphycercal.

8. The jaw suspension is autostylic.

9. The swim-bladder is modified into “lung”.

10. Viviparous.

The subclass crossopterygii is divided into two superorders: (A) Osteolepides (Rhipidistia) and (B) Coelacanthi.

Superorder (A) Osteolepides (Rhipidistia) (Lower Devonian — Upper Carboniferous):

1. Caudal fin heterocercal or diphycercal, never consisting of three lobes.

2. Scales are with an outer layer of cosmine. It includes two orders:

Order (1) Osteolepiformes:

1. The paired fins are with a short rounded lobe.

2. Scales are covered with cosmine. Example: Osteolepis (Fig. 6.59C).

Order (2) Rhizodontiformes:

1. The paired fins are with a short rounded lobe.

2. Scales are cycloid and thin.

Example: Eusthenopteron (Fig. 6.59B), Rhizodus.

Superorder (B) Coelacanthi:

1. The crossopterygians in which the body is covered with thin cycloid scales.

2. The caudal fin is diphycercal consisting of three lobes.

3. Teeth are of simple structure.

4. Air bladder is ossified.

5. Hyomandibular is reduced, not ossified.

It includes a single order:

Order (1) Coelacanthiformes (Actinistia) (Upper Devonian — Recent) [2 living species]:

1. The Coelacanthi in which the scale is cycloid and thin.

2. Teeth are of simple structure.

3. No vertebral centra except for the caudal region in some.

Examples:

Coelacanthus, Macropoma, Undina, Latimeria chalumnae Smith, 1939. Latimeria menadoensis has recorded in 1998, from the deep sea in between Borneo, Philippines and New Guinea.

Subclass (2) Actinopterygii (Middle Devonian — Recent) [Gk. aktino = ray + pterygo = fin or wing] [20,900 living species]:

The subclass Actinopterygii gets its name from the characteristic pattern of the paired fins. The ‘ray-finned bony fishes’ inhabiting seas or freshwater are included under the group.

The common features of this subclass Actinopterygii are:

1. Radials of pair fins are not arranged biserially.

2. Scales are not of cosmoid type.

3. Primitive forms possess a single dorsal fin.

4. The tail is mostly homocercal which may be semi heterocercal or heterocercal in a few forms.

5. The investing bones of the skull and jaws become greatly reduced in number in comparison to that of the crossoptery­gians.

6. Squamosal is absent.

7. Jugal sensory canal is wanting.

8. The internal nostrils and spiracles are absent.

There is a difference of opinion regarding the classification of Actinopterygii. The sub­class is usually divided into three groups (superorders), namely Chondrostei, Holostei and Teleostei. Goodrich (1909) divides the subclass Actinopterygii into two superorders—Chondrostei and Holostei. Regan (1923) again divides Actinopterygii into Palaeopterygii corresponding to chondrostei and Neopterygii that correspond to the Holostei and Teleostei.

But the remarkable researches of Stensio (1932) have shown that the Chondrostei gradually passes into the Holostei and that can be separated from the remaining orders only artificially. Likewise, the difference between Holostei and Teleostei is not prominent and the two groups merge gra­dually.

Hence, according to Berg (1940), if both the living and fossil forms are taken into con­sideration, the division of Actinopterygii into three superorders Chondrostei, Holostei and Teleostei becomes artificial. Berg has not, therefore, used these three groups and divided the Actinopterygii into a series of orders.

According to Patterson (1973), in recent years the Holostei is regarded as a grade of actinopterygian evolution whose upper and lower boundaries can be arbitrarily defined. As a result, the terms Holostei, Teleostei and Chondrostei have been dropped from most formal classifications.

All these terms have come to be regarded merely as a grade and in the classifications of Berg (1940, 1955) and Lehman (1966), all supra-ordinal groupings in Actinopterygii have dropped. Again with the publication of a phyletic classification of living teleosts in 1966 by Greenwood, Rosen, Weitzman and Myers, the trend has reversed.

Since then various cladistic (Phylogenetic) classifications of Actinopterygii have been expressed, but the older arrangement of different taxa based on grades is more plausible.

According to Berg (1940) the whole sub­class (Actinopterygii) is divided into two groups which include about sixty living and fossil orders. Here a description of only impor­tant orders is given.

Group A:

This group differs from all other actinopterygians in the structure of the pec­toral endoskeleton and of the dorsal fin. This group includes only the living order polypteriformes.

Order (1) Polypteriformes (Cladista, Brachiopterygii) [Bichirs and reed fishes] [9 living species]:

1. The body is covered with rhombic ganoid scales and provided externally with small denticles.

2. The dorsal fin possesses 8 or more finlets, each finlet being supported by a single radial.

3. The caudal fin is symmetrical, although not typically diphycercal.

4. Pectoral fins are with a small prominent base covered with scales. Fin-rays are supported by numerous ossified radials which, for their part, are attached to a cartilaginous plate and two elongated ossified rods articulating with the ossified scapula and coracoid.

5. A single spiracle persists and helps in the expulsion of excess water taken in the mouth cavity.

6. There are dorsal nostrils and the swim- bladder which is bilobed, unites into a single duct in front and opens into the pharynx by a median ventral aperture. The lung-like swim-bladder also acts as an accessory respiratory organ and helps the animal to survive during periodic drought.

7. There are four gill-arches. A pair of exter­nal gills are present which are peculiar in that they connect with the hyoid and developed from the skin.

8. The intestine has a well-developed spiral valve.

9. The notochord is reduced and replaced by bony vertebrae.

10. Choanae (internal nostrils) are absent.

Remarks:

The nature of scales, presence of spiracle, the structure of pectoral fins and arrangement of skull bones strongly suggest a palaeoniscid ancestry.

Family Polypteridae:

There are two known genera — Polypterus and Calamoichthys. Polypterus (bichir) includes eight species, one in the Nile, one in the Niger and six in the Congo. They are polypterus bichir, P. senegalus and P. lapradei etc. Calamoichthys has a single species — C. calabaricus (reedfish) is found in the Niger delta. They eat worms, insect larvae and small fishes.

Remarks:

Huxley and Woodward (1891) regarded polypterus as a member of Crossopterygii. Stensio (1932) claimed the polypteridae as a group in the subclass Teleostomi, equivalent to Crossopterygii and Actinopterygii, and for the group he proposed the name Brachiopterygii and this supported by Holmgren and Stensio in 1930 and Jarvik (1968). Goodrich (1930) places the polypteridae among the Actino­pterygii as an order equivalent to Chondrostei also accepted by Gardiner (1967), Miles in Moy-Thomas (1971).

Group B:

The actinopterygians in which the pectoral radials are attached at least partly, immediately to the scapulocoracoid cartilage or to the scapula and coracoid. Berg (1940) included 59 extinct and living orders and 562 extinct and living families under the group B.

Order (2) Tarasiiforms [Lower carboniferous]:

1. Caudal fin is diphycercal.

2. Dorsal is long, beginning not far behind the head, confluent with the caudal and anal.

3. No ventrals.

4. Notochord persistent and haemal arch ossified.

Examples:

Tarasius, Palaeophichthys

Order (3) Palaeonisciformes [Mid. Devonian — Lower Cretaceous]:

1. Ossified ribs are absent.

2. Scales are usually ganoid rhombic, and sometimes cycloid.

3. A single dorsal fin is present.

4. Dermal bones of the cranial roof are cove­red with ganoine.

5. The eyes are large in size and are provi­ded with four sclerotic plates. Although palaeoniscids arose from the same ances­tral stock from which crossopterygians evolved, the palaeoniscids differ greatly from the latter.

Examples:

Cheirolepis, Canobius, Plectrolepis, Palaenoniscus, Perleidus, Helichthys.

Order (4) Acipenseriformes [Sturgeons and Paddle fishes] 6 genera and 26 living species:

The members of Acipenseriformes include the sturgeons which have descended from the palaeoniscids and is characterised by the reduction of bones.

1. The snout is elongated.

2. The body is covered with five rows of bony scutes or naked.

3. The small mouth is ventrally placed and provided with barbels.

4. The jaws are weekly developed and are without teeth.

5. Caudal fin is heterocercal.

6. The tail is covered with small rhomboidal scales.

7. An open spiracle is present.

8. Endocranium is largely cartilaginous.

9. Pre-maxillary is fused with maxillary bone.

10. Clavicle is present.

11. Inter-orbital septum is absent.

12. Vertebral centra are absent.

13. Radials in the dorsal and anal fins are not ossified.

14. Notochord is present to a great degree.

The modern sturgeons inhabit the sea but migrate to the river for spawning (anadromous migration). They feed on invertebrates which are collected from the muddy bottom by stir­ring up with the snout. In general, they are sluggish and clumsy.

Families (1) Polyodontidae:

Polyodon spathula (Paddle fishes or spoon bill) — which lacks a protrusible mouth, inhabits in the rivers of Mississippi, Ohio and Missouri of N. America. Psephurus gladius which possesses a protrusible mouth and an inhabitant of Yangtse and Hoang Ho rivers of China.

(2) Acipenseridae:

Acipenser, Fig. 6.49B (typical sturgeon) — Europe, North America and Russia. Scaphirhynchus (Shovel nosed sturgeon) — North America and Central Asia.

Order (5) Amiiformes (Protospondyli) (Up Permian — Recent) [Bow fins]:

1. The tail is slightly heterocercal and the head is covered with a bony armour.

2. The scales have become reduced to bony cycloid type.

3. The swim-bladder is modified into a “bilobed dorsal lung”.

4. The spiral valve is vestigial.

5. Pre-maxillary is not protractile, firmly arti­culated with cranium.

6. The vertebrae are of amphicoelous type.

Families Amiidae:

It includes a single species — Amia calva, Fig. 6.48C (Bow fin or Crindle or John A. Grindle) — Lives in the Mississippi valley and Great Lakes of America.

Order (6) Pycnodontiformes:

1. The body is laterally compressed and covered by rhombic scales.

2. The tail region may lack scales.

3. The opercular apparatus is reduced.

Examples: Gyrodus, Coccodus, Pycnodus.

Order (7) Lepidosteiformes (Ginglymodi) (Up. Cretaceous — Recent) [Garpikes]:

1. Elongated body with a long snout.

2. The tail is nearly symmetrical.

3. The body is covered by thick rhomboidal ganoid scales.

4. The skeleton is well-ossified and there are 4-8 valves in the heart.

5. The vertebrae are opisthocoelus type.

6. The swim bladder is cellular and highly vascular and is connected to the pharynx by a pneumatic duct.

Family Lepidosteidae (Up. Cretaceous – Recent) (e.g., Lepidosteus (Fig. 6.48D) = Lepisosteus) — 1 genera and 4 species — occur from Quebec to the Mississippi valley and the Great Lakes, and in Central America.

Order (8) Pholidophoriformes (Mid. Tri. — Up. Cret.):

e.g., Pholidophorus, Archaeomaene.

Order (9) Clupeiformes (Isospondyli) [Herrings, sardines, anchovies, salmon and trouts] [Jurassic — Recent]:

1. The body covering scales are of cycloid type.

2. The tail fin is homocercal.

3. A single dorsal fin is present.

4. The ventral fin may be absent.

5. The fins are devoid of fin-rays. The weberian apparatus is lacking.

6. They are found in freshwater, seas and estuaries.

Family (1) Elopidae (Lady fishes):

Body elongated and fusiform; mouth termi­nal; a gular plate present; no spines in the fins; dorsal fin a little behind from the middle of the dorsal surface with 17 to 20 rays; pelvic fin a little ahead of dorsal fin; anal fins with 14-17 rays; 27-34 branchiostegal rays; no conus arteriosus.

Mainly marine, tropical and subtropical seas; single genus with 6 species. A single species Elops machnata (Fig. 6.60A) around the Indian coasts.

Family (2) Megalopidae (Tarpons):

Body elongated and fusiform; mouth termi­nal; a gular plate present; no spines in the fins; dorsal fin a little behind from a little behind of the midpoint of body with 13-21 rays and last dorsal fin-ray filamentous; pelvic fins a little ahead of dorsal fin origin with 10 or 11 rays; anal fins with 24-31 rays; conus arterio­sus with two rows of valves; 23-27 bran­chiostegal rays. Mainly, Indo-west pacific. Single genus, with a single species, Megalops cyprinoides Fig. 6.60B), found around the Indian coasts.

Family (3) Albulidae (Bone fishes):

Body elongated and fusiform; upper jaw projects beyond the tip of the lower jaw; small, sub-terminal mout; rudimentary or no gular plate; no spines; dorsal fin with 16-17 rays; anal fin with 7-9 rays; 10-15 bran­chiostegal rays; conus arteriosus with two rows of valves. Marine, Indo-west Pacific; Single genus Albula (Fig. 6.60C) with 3 species; Albula glossodonta and A. neoguinaica are found around the Indian coasts.

Family (4) Pterothrissidae:

As Albulidae; other characters are dorsal fin long with 55-65 rays; gular plate absent and 6 branchiostegal rays; conus arteriosus with two rows of valves. Marine, Eastern Atlantic Gulf; Single- genus, two species; e.g., Pterothrissus, not found in our coasts.

Family (5) Clupeidae (herrings, shads, sardines, sardinellas, sprats and pellonas):

Body small fusiform, sometimes strongly compressed body; sometimes scutes present along the body; no spiny rays in the fins; sin­gle short dorsal fin (absent in Raconda); gular plate absent; branchiostegal rays 6 or 7; cau­dal fin deeply forked; lateral line absent; teeth small or absent.

Marine or some fresh water and anadromous. Worldwide, mostly tropical. About 55 genera and 180 species. Some Indian species are Anodontostoma chacunda (Chakunda gizzard shad), Dussumiera acuta (Rainbow sardine).

Hilsa shad, Tenualosa ilisha (Fig. 6.60D), Fishes of the Ganges; Clupanodon ilisha. Dussumieria, Clupea, Sardina, Sardinella, Alosa, Cudusia, Hilsa, Anodontostoma, Dorosoma, Gonialosa – all are Indian genera.

Family (6) Engraulidae (Anchovies):

Small, fusiform, sometimes strongly com­prised body; scutes present along the abdomen (absent in Engraulis); upper jaw extended far forward than the lower jaw; no spiny rays in fins; pelvic fin originates anterior to dorsal fin origin; anal fin rays more than 15; caudal fin generally forked; no lateral line; silvery colour. Marine and freshwater; Indo-Pacific and Atlantic. 16 genera with 135 species. Coilia, Setipinna, Stolephorus, Anchovia, Engraulus (Fig. 6.60E) etc.

Indian species are Coilia dussumieri (Gold spotted grenadier anchovy), Stolephorus indicus (Indian anchovy) etc.

Family (7) Chirocentridae (Wolf-herrings):

Very elongated and highly compressed body; scutes absent along the abdomen; well-developed canine teeth in both jaws; no spiny rays in fins; dorsal fin single, develops far behind the mid-point of the dorsum and with 16-19 rays; anal fin with 30 – 50 rays; cau­dal fin deeply forked. Marine, Indo-west Pacific. One genus with two species (Chirocentrus dorab, Wolf herring, Fig. 6.60F) and C. nudus) found along Indian coasts.

Family (7) Chanidae (Milk fish):

Elongated and moderately compressed body; small mouth, without teeth; no spines in the fins; dorsal fin at the midpoint of the body; no gular plate; 4 branchiostegal rays; scales cycloid or ctenoid.

Marine, Indo-Pacific. Chanos chanos is the only species found around the Indian coasts.

Family (8) Salmonidae [Trout]:

Elongated and slightly compressed body; scales on the whole body except head; adipose dorsal fin with a single ray; barbels absent; 12 vertical bands on the body surface; dorsal sur­face with black spots; 7-20 branchiostegal rays; last vertebrae up-turned.

Fresh water, anadromous of Northern Hemisphere. 11 genera with 65 species. Salmo, Onycorhynchus, Stenodus, Hucho, etc.

Salmo gairdnerii — a native of California introduced into Kashmir and Nilgiris.

Family (9) Notopteridae:

Elongated, large forms and highly com­pressed body; body covered with minute scales; dorsal fin small or absent; anal fin long and continuous with the reduced caudal fin; silvery body colour with small black spots on the posterior part of the body. 4 genera with 8 species (e.g., Notopterus (Fig. 6.60G) — Fresh water of India, Tropical Africa; N. notopterus (Folui), N. chitala (Feather back, Chital, both found in Indian waters).

Family (10) Hapiochitonidae:

Adipose fin present; dorsal fin with 11-14 rays; caudal fin forked; branchiostegal rays 3 or 4. (e.g., Haplochiton — South America).

Order (10) Esociformes (Haplomi) [Pikes, muminnows and beaked salmon] [Miocene- Recent]:

1. The fins are provided with soft rays.

2. The pyloric caeca are absent.

Berg (1940) mentioned Esocoidei as a suborder under order clupeiformes but C. T. Regan (1925) places Esocoidei or Haplomi as separate order.

Families:

(i) Umbridae (e.g., Umbra – Mud-minnow of North America),

(ii) Dalliidae (e.g., Dallia (Black of Alaska, N. E. Siberia),

(iii) Esocidae (e.g., Esox – Europe and N. Asia).

Order (11) Bathyclupeiformes:

1. Ventral fins thoracic, 1, 5 with a spine.

2. Dorsal fin single without spines.

3. Anal long with a spine.

4, Vertebrae 31.

5. Deep sea fishes.

Family Bathyclupeidae (e.g. Bathyclupea — Indian, Western Pacific and Mexican Gulf).

Order (12) Galaxiiformes:

1. Adipose fins are lacking.

2. Pectorals are placed low.

3. Maxillary bones are toothless, to a certain extent.

4. Orbitosphenoid are absent.

Family Galaxiidae (e.g., Galaxias—Southern Hemisphere).

Order (13) Scopeliformes (Iniomi) [Lantern and Lizard fishes] [Cretaceous — Recent]:

1. The mouth is wide and armed with numerous minute teeth.

2. The dorsal and ventral fins are lacking spines.

3. The body is almost cylindrical.

4. The swim-bladder is usually absent.

5. Adipose fin are usually present.

6. Ventral fins are with 6-13 rays. Most of the fishes possess phosphorescent organs which develop by the modification of the integumentary glands. Most are deep sea forms.

Family (1) Synodidae (Synodontidae) (Lizard fishes):

Supramaxilla small or absent; branchio­stegal rays 8-26. Nelson (1994) divides the Synodidae into 2 subfamilies — (i) Synodontinae which includes Synodus and Trachino- cephalus, and (ii) Harpadontinae includes Harpadon (Fig. 6.61 A) and Saurida.

In FAO species identification sheets (West Indian Ocean – Fishing Area 51) it is seen that there are two separate families — (i) Synodontidae which includes Saurida, Synodus and Trachinocephalus and (ii) Harpadontidae includes only Harpadon.

In Synodontidae (lizard fishes) the lateral line is confined to the body, not extending as median lobe of caudal fin which is found in Harpadon­tidae (Bombay duck). Nelson (1994) includes synodontidae under the order Ateleopodiformes.

Marine, Indo-pacific and Atlantic.

Harpodon nehereus (Fig. 6.61 A) (Bombay duck — Only Indian species found from India to China).

Family:

(ii) Omosudidae (Omosudids) (e.g., Omosudis — Atlantic and Indian).

Order (14) Ateleopiformes [Ateleopus]:

1. There are no adipose fins.

2. Ventral fins are with 1-2 rays.

3. Pectoral radials are represented by a sin­gle cartilaginous plate.

4. Air-bladder is absent.

5. Pelvis is scarcely ossified articulated to coracoids.

6. Deep sea forms.

Family Ateleopidae (e.g., Ateleopus, Parateleopus — Atlantic, Indian and Pacific).

Order (15) Giganturiformes (Giganturoidea) [Deep sea giganturids]:

1. Ventral fins are absent.

2. Eyes are teleoscopic.

3. Fin-rays are un-branched,

4. Pectorals are placed high with 29-43 rays.

5. Gill openings are small.

Family Giganturidae (e.g., Gigantura – deep sea fishes).

Order (16) Saccopharyngiformes (Lyomeri) [Gutper eels]:

1. Jaws are very large.

2. Pharynx is enormous and distensible.

3. Ventral fins are absent.

4. Fins are spineless.

5. Air bladder absent.

6. Peculiar luminous organs are present.

7. Deep sea forms.

Families:

(i) Saccopharyngidae (e.g., Sacco- pharynx),

(ii) Eupharyngidae (e.g., Eupharynx).

Order (17) Mormyriformes [Mormyrids]:

1. As Clupeiformes but cerebellum is large.

2. Palatines are fused to vomer.

3. Opercular bones are concealed below skin.

4. Some have finger shaped processes on the jaw, used as feelers. Some possess weak electric organs.

Families (i) Mormyridae (e.g., Mormyrops — Africa), (ii) Gymnarchidae (e.g., Gymnarchus — Nile, Africa).

Order (18) Cypriniformes (Ostariophysi) [Carps, Catfishes, Piranha]:

1. The fins are usually absent or provided with spine.

2. The ventral fin is abdominal in position.

3. The swim bladder is connected with the gut by a duct.

4. Weberian apparatus is present between the ear and the swim bladder.

5. Mouth toothless.

6. Upper jaw is usually protractile.

7. Adipose fin absent (except in some cobitoids).

Freshwater, worldwide; about 6500 spe­cies. Berg (1940) divided the order into two divisions and C. T. Regan admitted this. The representatives of the order are placed under two divisions.

Division I. Cyprini (Gk. Cyprin, Carp):

The body is covered with scales or naked, never covered with bony plates.

Some of the families with Indian examples are:

Family (1) Cyprinidae (Carps):

Lips thin; upper lip usually protractile; scales absent on the head region; barbels pre­sent or absent, if present not more than 4; spine-like rays in dorsal fin in some; pharyn­geal teeth one to three rows, highest number in one row 8. Mainly freshwater, rarely in brackish water; Asia, Europe, Africa and some regions of U.S.A. About 210 genera and about 2,010 species.

Examples : Oxygaster gora (Freshwater forms in W. Bengal, Orissa, Assam and Punjab); Rasabora daniconius (Dankoni) – Slow stream forms in N. Bengal; Barilius bola (Indian Hill trout; Chief game fish in Assam rivers, also found in N. Bengal and Orissa); Labeo bata (Bata); L. calbasu (Kalbose); Cirrhina mrigala (Mrigale); C. cirrhosa (white carp of S. India); C. reba (Bata – found in the Tarai and Duars of N. Bengal); Carassius carrassius (wild gold fish – European Carp); Cyprinus carpio (Common Carp – a pond fish of China and S. E. Asian countries, was intro­duced into Nilgiris from Sri Lanka); Catla catla (Katla); Puntius curmuca (Buchanan’s Carp – waters on Western Ghats, Malabar plains and Madurai); P. sarana (Swarna puti — rivers and ponds all over India); Tor tor (Tor, Mahasar — North India).

Other families are:

(ii) Characinidae (e.g., Hydrocyon – Freshwater of Africa; Myleus, Myletes – Freshwater of South America), (iii) Catostomidae (e.g., Cycleptus – North America) (iv) Gymnotidae (e.g., Gymnotus – Guatemala).

Family Electrophoridae (Electric knife fish):

Electric organs are formed by the modi­fication of muscular tissues on the side of the tail region. One species in Amazon river – Electrophorus electricus.

Family Cobitidae (Loaches):

Small, cylindrical body; mouth sub-terminal; 3-6 pairs of barbels; single row of pha­ryngeal teeth; thick fleshy lips. Freshwater, high altitudes or plain zones; Asia, Morocco and Europe. About 8 genera and 110 species. 8 species known from India. Lepidocephalus guntea occurs throughout India and L. thermales restricted to S. India.

Division 2. Siluri (L. a kind of river fish):

1. The body is naked or covered with bony plates.

2. The reduced maxillary bone supports the barbels.

3. The second, third, fourth and fifth verte­brae are fused.

4. Parietals are absent.

Some of the families with Indian examples are:

Family Ariidae (Tachysuridae) (sea catfish):

Median to large sized naked fishes; head round to depressed; teeth in jaws; barbels 1-3 pairs and usually 2 pairs of mental barbels and 1 pair maxillary; head covered with a bony shield; first dorsal fin spine-like, often serrated; pectoral fin with a serrated spine with 7-13 rays; anal fin with 14 to 30 rays; tail forked.

Marine, brackish and freshwaters; tempe­rate and tropical regions. About 14 genera and 120 species, (e.g., Tachysurus – Sea cafish). T. jella – common on the east coast; T. sona – throughout Indian coast. Engraved catfish, Arius (Tachysurus) caelatus; Sagar catfish, A. sagor (Fig. 6.61 B); Giant catfish, A. thalassinus; Spotted cat fish, A. maculatus; Threadfin catfish, A. arius; Blacktip sea cat­fish, A. dussumieri, etc. found around Indian sea coasts.

Family Clariidae (Air breathing catfishes):

4 pairs of barbels; dorsal fin very long and without spines, more than 30 rays; pectoral fins with serrated spines; anal fin also long, not connected with caudal fin; caudal fin more or less rounded. Freshwater, S. East Asia and Africa; About 13 genera and 100 species, (e.g., Clarias batrachus – (Freshwater form in India).

Family Heteropneustidae (Air sac catfishes):

Four pairs of long barbels; dorsal fin small and spineless; anal fin very long; pectoral fins with poison spine.

Freshwater, India, Bangladesh, Sri Lanka and Myanmar (Burma). Single genus with two species (e.g., Heteropneustes fossilis and H. microps).

Family Siluridae (Sheat fish):

Small to larger forms; laterally com­pressed and naked body; 3 pairs of barbels; adipose dorsal fin absent or short; anal fin very long and with 41-110 rays; dorsal fin without spine and with 4 to 5 rays; caudal fin usually forked.

Freshwater, Asia and Europe; 12 genera and 100 species. Ompok, Wallago, Silurus, Hemisilurus, Hito etc. (e.g., Ompok pabo (Pabda), Wallago attu (Boal), Ompok bimaculatus – Indian freshwater.

Family Sisoridae (Bagaridae) (Sucker catfish):

Elongated and naked body, depressed anteriorly; tail compressed; mouth toothless; four pairs barbels; adipose dorsal in addition to dorsal fin with nine spines; caudal fin forked; ventral surface with an adhesive organ in some cases. Freshwater, some found in hill-streams; Asia. 20 genera and 80 species. Bagarius, Gagata, Hara etc.

Bagarius bagarius, (Fig. 6.61 C); Gagata cenia – India).

Family Bagridae (Bagrid catfish):

Body more or less elongated; head depressed; 4 pairs of barbels; first dorsal fin with a spine and with 6-8 rays; pectoral fin with a spine; anal fin long with 25-28 rays; teeth or palate villiform.

Freshwater, marine (only single Mystus gulio); Asia and Africa. 12 genera and 205 species – Mystus aor – throughout India; Rita rita – freshwaters of India; M. seenghala (Fig. 6.61 D); M. vittatus; M. cavasius found in India.

Family Plotosidae (Cat fish eels):

Scaleless, elongated body, tapers posterior­ly. 2 pairs widely separated nostrils; first small dorsal fin with a serrated spine; second dorsal fin with 69-142 rays; anal fin very long and confluent with the caudal fin; pectoral fin with a serrated spine; body colour brown or black at the upper sides, ventral side white or pale.

Chiefly marine, Indo-pacific. 9 genera and 32 species. Plotosus, Oloplotosus, Cnidoglenis etc. (e.g. Plotosus anguillaris, P. limbatus (Fig. 6.61 E) – seas of Indo-pacific region).

Family Malaptiruridae (Electric catfish):

3 pairs barbels; dorsal fin absent; caudal fin rounded; a subcutaneous electric organ is present.

Freshwater, Africa. Single genus with 2 spcies (e.g., Malapterurus – Africa).

Family Pangasiidae:

Large-sized compressed body; 2 pairs barbels; dorsal fin with a spine and with 5-7 soft rays; anal fin long with 26 to 46 rays, not confluent with caudal fin; caudal fin with 30-34 rays; adipose fin present.

Freshwater; South-east Asia; 2 genera and 19 species. Pangasius and Helicophagus.

Family Olyridae:

Elongated naked body; 4 pairs of barbels; dorsal fin without a spine; pectoral fin with a serrated spine and fin moderately long with 16-23 rays; caudal fin long or forked.

Freshwater; India and Myanmar. Single genus with 4 species; Olyra.

Family Chacidae (Frogmouth cat fish):

Large sized body; 3 pairs of barbels; abdomen flat; dorsal fin with a spine and with 3-4 rays; pectoral fin with a serrated spine and with 4-5 rays; anal with 7-10 rays.

Freshwater; India and Indo-Malayan Archi­pelago. One genus with 3 species; e.g., Chaca.

Family Schilbeidae (Schilbeid cat fish):

Body short, elongated and compressed; head oval, blunt or conical; barbels 1 pair, 2 pairs or 4 pairs; first dorsal fin with a spine; pectoral fin with a serrated spine; anal fin long, not confluent with caudal fin and with 24-29 rays; short adipose dorsal fin. Freshwater; India, Africa, Indo-China and Indo-Malayan Archipelago; 18 genera and 45 species; e.g., Clupisoma, Silonia, Ailia, Physailia etc.

Order (19) Anguilliformes (Apodes) [Eels]:

1. Body is very elongated.

2. Fins are without spines.

3. Pelvic fins are absent.

4. Body is naked, except Anguilla where minute scales are present.

Families:

1. Anguillidae (Freshwater eels):

Elongated, cylindrical body with small oval- shaped scales; lower jaw projecting slightly; dorsal, anal and caudal fins confluent each other; compressed tail; small, conical teeth.

Freshwater and brackish waters but migrating into seas for spawning. Single genus with 15 species.

Indian examples. Anguilla bengalensis (Fig. 6.62A), A. bicolar, A. marmorata etc.

2. Congridae (Conger eels):

Extremely long body; no scales; lower jaw equal to or smaller than upper jaw; dorsal and anal fin confluent in most cases. Marine, tropical seas. About 150 species. Indian example. Uroconger lep- turus (Indian coasts).

3. Muraenesocidae (Pike congers), Congresox talabon (Gulf of Manner, eastern coast), C. talabonoides (Indian coasts).

4. Muraenidae (Morays):

No scales; no pectoral fins; skin tough and thick; large mouth with lager molar-like teeth; vertical slit-like gill openings; typically spotted, banded, or mottled.

Marine; tropical and temperate seas; 15 genera and more than 150 species.

Indian example:

Gymnothorax (Morays) (Fig. 6.62B), Echidna nebulosa (Starry moray), E. zebra (Zebra moray, Gulf of Mannar, West coast). Thyrsoidea macrura (Giant slender moray, Indo-Pacific), Lycodontis meleagris (Turkey moray, tropical Indo-west Pacific).

Order (20) Halosauriformes (Lyopomi):

1. The body is slender.

2. The tail is long but without caudal fin.

3. They have no spiny fins.

Family Halosauridae. Halosaurus (deep sea forms).

Order (21) Notacanthiformes (Heteromi) [Spiny eels]:

1. Elongated bodies are terminated in a point.

2. Pectorals are placed high on the flanks.

3. Scales are cycloid and minute.

4. Anal fin is long and extends to the end of the body.

5. Deep sea forms.

Families:

1. Notacanthidae (Spiny eels): Notacanthus (All oceans).

2. Lipogenyidae: Lipogenys (Atlantic).

Order (22) Beloniformes (Synentognathi) [Skippers and flying fishes]:

1. Snout beak-like with upper and or lower jaws greatly prolonged except 2 genera.

2. Wing-like pectorals and sometimes pelvic fins.

3. A single dorsal fin.

4. Pelvic fins are abdominal.

5. Physoclistic.

6. Fins without spines.

Family Belonidae (Needle fishes):

Elongated body; both jaws highly extended into long beaks with teeth; dorsal and anal fins posterior in position; pelvic fins abdominal with 6 soft rays.

Marine, few occur in freshwater. 10 genera with 32 species. (Tylosurus, Belone, Xenentodon, Strongyluras, Fig. 6.62C; Ablennes, Platybelone —> Indo-Pacific).

Family Hemiramphidae (Half beaks):

Elongated body with short upper jaw; lower jaw highly prolonged except Oxyporhamphus; dorsal and anal fins posterior in position; pelvic fins short with 6 rays. Mostly are marine, a few are freshwater. 12 genera with 82 species. Hemiramphanodon occurs in freshwater. (Hemiramphus, Fig. 6.62D; Hyporamphus, Oxyporamphus – Tropical and subtropical seas).

Family Exocoetidae (Flying fishes):

Elongated bodies; no spines in the fins; pectoral fins highly developed that extend beyond dorsal fin origin; pelvic fins abdomi­nal and enlarged in some species; lateral line low on body; caudal fin unequally forked with lower lobe longer than the higher lobe.

Marine, tropical and subtropical; 7 genera and 50 species. (Exocoetus (Fig. 6.49A) Parexocoetus, Cypselurus—warmer seas).

Order (23) Gadiformes or Anacanthini [Cods, hakes, haddocks and whiting]:

1. Pelvic fins are in front of the pectorals.

2. The body is covered with cycloid scales and a lateral line is present.

3. There is a closed swim-bladder.

Family Bregmacerotidae (Codlets):

Body elongated with short head; two dorsal fins, the first dorsal fin longer, with a single ray on the head; the second dorsal fin long; anal fin like second dorsal fin much longer; pelvic fins much longer than the 1st dorsal fin.

1 genus with 12 species. Bregmaceros (Tropical and subtropical seas).

Family Gadidae:

Gadus (whiting), Melono- grammus (Haddock) etc. Tropical seas.

Order (24) Macruriformes [Rat tails]:

1. First dorsal fin sometimes with a spine.

2. Scales cycloid or ctenoid.

3. Caudal fin symmetrical confluent with dorsal and anal.

4. Deep sea forms.

Family Macrouroididae:

Macrourus (North Atlantic, Pacific).

Order (25) Gasterosteiformes (Thoracostei) [Stickle backs, indostomids]:

1. The fishes are small with a closed swim- bladder.

2. There are several free spines in front of the dorsal fin.

Families:

(i) Gasterosteidae: Gasterosteus (Northern Hemisphere)

(ii) Indostomidae: Indostomius [Freshwater lakes in Upper Myanmar (Burma) and India).

Order (26) Syngnathiformes (Solenichthyes) [Flute fishes, Pipe fishes and Sea horse]:

1. The mouth is placed at the tip of tubular snout.

2. The body is covered with scales and some­times modified into series of bony plates.

3. Males possess a brood pouch in sea horse and pipe fishes.

Family Aulostomidae (Trumpet fishes):

Elongated body, barbel present on lower jaw; both jaws moderately elongated; com­pressed body; distinct separate spines anterior to soft dorsal fin.

Marine, tropical and subtropical; single genus with 3 species. Aulostomus (Tropical, Atlantic, Indo-Pacific).

Aulostomus chinensis occurs in the south­ern coasts of India and Sri Lanka.

Family Fistulariidae (Flute fishes):

Body elongated and depressed; long tubu­lar snout with small teeth in jaws; rides on snout with serrations; dorsal and anal fins short, posterior of the body and opposite each other; pectorals with 15 or 16 rays; bony plates on mid line; a caudal filament is present.

Marine, tropical and subtropical; single genus with 4 species. Flute fish, Fistularia (Tropical seas).

Fistularia petimba and F. commersonii occur around Indian coasts.

Family Centriscidae (Razorfish):

Extremely compressed razor-like fish; first dorsal spine at the end of the body; mouth toothless.

Marine, tropical; 3 genera with 3 species.

Razorfish, Centriscus (Amphisile) scutatus, Fig. 6.63A (Indo-Pacific).

Family Syngnathidae (Pipefish, Sea horse):

Two nasal openings on each side; body covered with dermal plates; dorsal fin if pre­sent single; fins without spines; anal fin if pre­sent rudimentary; caudal also if present, very small and caudal peduncle may be prehensile.

Marine, brackish water and some freshwa­ter; Indo-pacific and Atlantic ocean. 52 genera and 210 species. Pipefish, Syngnathus, Fig. 6.50A;, Dorichthyes; Sea horse, Hippocampus, Fig. 6.50D (widely distributed in all seas).

Some Indian species are: Syngnathus carce (Freshwater pipefish); S. brachyurus (Short tailed pipefish) and Hippocampus kuda. Dorichthys cunculus enters into the rivers.

Order (27) Lampridiformes (Allotriognathi) [Moonfish, Ribbonfish]:

1. The fishes are marine.

2. The eyes are large.

3. The teeth are feebly developed or absent.

Families:

(i) Lampridae (e.g., Lampris – distributed in all seas),

(ii) Veliferidae (Veliferids) (e.g., Velifer— Indo-Pacific).

Order (28) Cyprinodontiformes (Microcyprini) [Cyprinodonts]:

1. The order includes small sized fishes where the pelvic fins may be absent.

2. The fins are spineless.

3. The mouth is protractile.

4. There is a single dorsal fin.

Families:

1. Cyprinodontidae (e.g., Cyprinodon, Aplocheilus panchax (Fig. 6.63 B), Cavefish Typhlichthys orestias — Indo- Malay, S. Europe, Africa, N. and S. America. 2. Poecilidae (e.g., Gambusia affinis (Top min­nows-introduced in India).

Order (29) Phallostethiformes:

1. The dorsal fins usually anterior consisting of 1 or 2 spines only.

2. Other fins are spineless.

3. Ventral fins are absent or rudimentary.

Families:

1. Phallostethidae (e.g., Phallos- tethus).

2. Neostethidae e.g., Neostethus – both genera found in brackishwater of Malay Peninsula, Thailand and Philippines.

Order (30) Percopsiformes (Salmopercae) [Sand rollers]:

1. Mouth is small and non-protractile.

2. Dorsal fin has two spines and the anal has one or two.

Families:

1. Percopsidae (e.g., Percopsis); 2. Rondelefidae (e.g., Rondeletia) — Both from freshwaters of N. America.

Order (31) Stephanoberyciformes [Prickle fishes, big scales, whale fishes]:

1. Fins are without spines.

2. Ventrals are abdominal or subabdominal with 5 or 6 rays. Deep sea forms.

Family Stephanoberycidae (e.g., Stephano- beryx)

Order (32) Beryciformes or Berycomorphi [Squirrelfish, Beardfish]:

The pelvic fins bear more than 5 soft rays.

Families:

1. Monocentridae (Pine cone fishes) (e.g., Monocentris — Indo-Pacific).

2. Berycidae (Alfonsinos) (e.g., Beryx— Indo- Pacific, Atlantic).

Order (33) Zeiformes or Zeomorphi [Dories and Boarfishes]:

The anal fins are preceded by one to four spines which form separate fins.

Families:

1. Zeidae (Dories) (e.g., Zeus faber, Fig, 6.63C, Parazen pacificus (Fig, 6.63D) — Mediterranean).

2. Carpoidae (Boar fish) (e.g. Antigonia — Tropical and temperate waters).

Order (34) Mugiliformes [Barracudas, mullets, silver sides]:

1. The order is recognised by their abdomi­nal pelvic fins.

2. Cycloid or ctenoid scales cover the body and the head is covered by scales.

Family 1. Sphyraenidae (Barracudas):

Body elongated and depressed; long poin­ted snout; lower jaw projecting the upper; strong teeth in the jaws; dorsal fin widely separated; first with 5 strong spines; forked caudal fin.

Marine, sometimes enters into brackish water, tropical and subtropical; single genus and 18 species (e.g., Sphyraena — all warm seas).

Indian species are Sphyraena jello, S. bar­racuda, S. forsteri, S. obtusata — Bay of Bengal and west Indian coast.

Family 2. Mugilidae (Mullets):

Elongated body with slightly depressed head; eyes often partly covered by adipose tis­sue; small mouth; two short dorsal fins, first with 4-slender spines; anal with 2-3 spines; caudal fin, moderately forked, no lateral line. Marine and brackish water, tropical and temperate seas. 1 7 genera and 65 species. Liza, Mugil, Valmugil etc. — warm and temperate seas.

Indian species – Liza tade Forskal, 1775 (Bhangan, Tade mullet); Liza subviridis (Valenciennes, 1836); Mugil dussumieri Valenciennes, 1836; M. Jerdoni Day 1876 (Green back mullet); Liza vaigiensis Quoy and Gaimard, 1824 — Square tail mullet; Mugil cephalus Linn. 1758 — Flat head mullet; Liza parsia (Ham. Buch. 1822 — Parse, parsia, Tarui, Gold spot mullet); etc.

Family 3. Antherinidae (Silver sides) (e.g., Antherina — Tropical and sub-tropical coastal waters.

Order (35) Polynemiformes [Thread fins]:

1. Pectoral fin is divided into two parts, the lower part being composed of long fila­mentous rays which are sometimes longer than the body.

2. Lateral fin extends to the caudal fin.

3. Dorsal fin has 8 spiny rays.

4. Scales are ctenoid.

It has a single family.

Family Polynemidae (Thread fins):

Medium-sized fishes with compressed body; scaly head with a conical, projecting upper snout; two widely separated dorsal fins, first with 7-8 week spines; pectoral fins with two parts, upper normal, the lower with 3 or more filamentous rays; lateral line extends on to caudal fine; caudal fin deeply forked.

Marine and brackish water; tropical and subtropical seas. 7 genera with 30 species, (e.g., Polynemus — Tropical, Indian, Atlantic and Pacific). Indian species are P. paradiseus (Tapse, paradise thread fin); P. indicus (Indian threadfin); P. sextarius (Black spot threadfin); P. heptadactylus (seven-finger threadfin); Eleutheronema tetradactylum (Gurjali, Four-finger threadfin).

Order (36) Ophiocephaliformes or Channiformes [Snakehead-fish]:

1. The head is depressed and covered by large plate-like scales.

2. Fins are without spines.

3. Scales are cycloid.

4. Air bladder very long, prolonged into cau­dal region, bifid posteriorly.

5. The accessory respiratory organ (supra- branchial organ) is present.

Family Ophiocephalidae (Channidae):

Body elongated; snout blunt or conical; long dorsal and anal fins; pelvic fins with 6 rays; no spines in the fins; cycloid or ctenoid scales on the body; lower-jaw protruding.

Freshwater, sometimes brackish; 2 genera, 21 species (e.g., Channa (Ophiocephalus) and Parachanna). (e.g., Ophiocephalus (Channa)— Freshwater fishes of S. E. Asia, Indo-Australian Archipelago. Indian species are Channa gachua (Cheng in Beng.), C. punctatus (Lata in Beng.), C. striatus (Sole in Beng.), C. marulius (Sal in Beng.). C. leucopunctus — both coasts of India and in inland waters in Kolhapur, Deccan).

Order (37) Synbranchiformes (Symbranchii) [Swamp eels, Cuchias]:

1. The body is eel-like.

2. There are no spines in the fins.

3. Dorsal, caudal and anal fins are conti­nuous.

4. Caudal fin if present with 8-10 rays.

5. Air bladder is absent.

Families:

1. Synbranchidae (Swamp eels) (e.g., Symbranchus—Gills 4, well developed— Tropical parts of all continents. 2. Amphipnoidae (Cuchias) (e.g., Amphipnous — (Two lung like air sacs — Freshwaters of S. E. Asia).

Indian species are — Symbranchus bengalensis (Fig. 6.63E) and Amphipnous cuchia.

Order (38) Perciformes (Percomorphi) [Perches, mackerels, croakers, archer fishes]:

The fishes belonging to this order are called Perches.

1. The dorsal and anal fins are provided with both spiny and soft fin rays

2. Two dorsal fins are present.

3. Scales ctenoid

4. The pelvic fins are either under, or in front of the pectoral fins

5. The swim bladder lacks a duct

6. The Weberian apparatus is lacking.

Many of the fishes in the order are of considerable economic importance, e.g., the mackerels, tunas and perches.

Family (1) Centropomidae:

Body elongated, compressed; mouth large, jaw equal or unequal; dorsal fin notched into two, first dorsal with 7 or 8 strong spines; 2nd dorsal with single small spine with 10-15 soft rays; anal with 3 species; lateral line extends up to last part of caudal fin; caudal fin rounded. Marine, often brackish; Indo-Pacific and Atlantic; 3 genera with 22 species, (e.g., Lates calcarifer (Bhetki, Barramundi—Bay of Bengal, Western Central pacific, Arabian sea.

Family (2) Serranidae (Rock perches) (e.g., Epinephelus)

Family (3) Theraponidae (Indo-Pacific) e.g., Therapon jarbua, Jarbua therapon)

Family (4) Trichiuridae (Hair tail fish) (e.g., Aphanopus, Lepidopus, Lepturacanthus, Trichiurus, Eupleurogrammus — Indo-Pacific).

Indian species are — Trichiurus haumela; T. gangeticus; T. savala, T. lepturus (Fig. 6.63F), etc.

Family (5) Toxotidae:

Body laterally compressed; mouth mode­rate in size; large eyes; single dorsal fin with 5 spines and 12-14 rays; anal fin with 3 spines; caudal fin straight.

Marine, Indo-Pacific; Single genus with 2 species, (e.g., Toxotes chatareus (Fig. 6.64A) — Archer fish).

Family (6) Sciaenidae (Croakers, Jewfishes):

Elongated, moderately compressed bod­ies; rostral pores often present, sometimes- marginal and mental pores; usually 3-5 rostral pores in snout, scales cycloid and ctemoid and on body and head; mouth terminal and sub- terminal; teeth generally small; dorsal fin long, continuous with a notch, anterior part with spines (8-10) and posterior part with a single spine and with 21-34 soft rays; pectoral with 16-18 rays; lateral line continuous on caudal fin; caudal fin different in shape.

Marine, brackish and fresh waters; Indo- Pacific and Atlantic. About 70 genera and 270 species (Nelson, 1994). Indian species are — Sciaena coibor, Johnius belangerii, J. dussumieri, J. macro- pterus (Fig. 6.64A), Nibea aibida, Otolithes ruber, Protonibea diacanthus (Fig. 6.64B) Pama pama, etc.

Family (7) Scatophagidae (e.g., Scatophagas argus — Indian coasts (spotted scat).

Family (8) Carangiidae (e.g., Caranx, Caran- goides, Scomberoides, Selaroides, Seriola — Tropical and subtropical waters).

Family (9) Cichlidae (e.g., Tilapia mossambica, Etroplus suratensis (Pearl spot) — Fresh and marine water tropical fishes.

Family (10) Scombridae (Mackerels):

Body elongated, medium to large sized, compressed in some genera; adipose tissue on eye-lid in some cases; two dorsal fins separa­ted by a space; finlets present behind 2nd dor­sal and anal fins; caudal fin deeply forked with caudal keels on the peduncle of the caudal fin.

Marine, tropical and subtropical seas. Differnt genera are Scomber, Rastrelliger, Acanthocybium, Scomberomorus, Gramma- torcynus, etc.

Indian species are — Rastrelliger kana- gurta (Fig. 6.64C), Scomberomorus lineolatus (Fig. 6.64D), S. commerson (Fig. 6.64E), S. guttatus, Acathocybium solandri, etc.

Family (11) Formionidae (Pomfret):

Remark:

W. F. Smith-Vaniz (1984) in F.A.O. species Identification sheet places Formio rtiger (Bloch, 1795) under Carangidae as Parastromateus niger (Bloch, 1795). e.g., Formio niger— Black pomfret.

Family (12) Stromateidae (Pomfret):

Body very deep and compressed; snout short and blunt; eyes with adipose tissue; mouth small and sub-terminal; scales small and cycloid, but head naked; single dorsal and anal fins; pectoral fins large and wing-like; caudal fin deeply forked; short caudal peduncle. Marine, Indo-Pacific. Single genera and two species (Pampus argenteus and P. chinen- sis). e.g., Pampus argenteus, Fig. 6.65B (silver pomfret); Pampus chinensis (Fig. 6.65C) (Chinese pomfret).

Family (13) Anabantidae:

Upper jaw weakly protrusible; mouth relatively large; jaws and vomer with conical teeth; body with ctenoid scales except Sandelia.

Freshwater and brackish water. South-east Asia and Africa.

Indian example:

Anabas testudineus, Colisa fasciatus.

Family (14) Gobiidae (Gobey):

Body with cycloid or ctenoid scales; pelvic fins well- developed, usually used for locomotion; dor­sal fin with 2-8 flexible spines. Marine and brackish water; occasionally freshwater. Tropical and subtropical.

Indian example: Clossogobius giuris (Fig. 6.65B).

Family (15) Chaetodontidae (Butterfly fish) (e.g., Chaetodon, Fig. 6.65E — Tropical waters).

Family (16) Periophthalmidae (Mudskippers) (e.g., Periophthalmus, Boleophthalmus — Coastal, brackish and freshwater of India.

Order (39) Dactylopteriformes [Flying gurnard]:

1. Pectorals are very large and subdivided into two portions.

2. Head is heavily armoured.

3. Eyes are large.

4. A small movable bone is between plate­-like bones around eye and preopercle.

5. Soft portion of dorsal fin is with 8 rays.

Family Dactylopteridae (Flying gurnard) (e.g., Dactylopterus — Tropical and subtropical seas). D. orientalis, Fig. 6.65A (Oriental flying gurnard), D. macrocanthus (Spot-wing flying gurnard) are Indian species.

Order (40) Thunniformes [Tunas or tunnies]:

1. They have a well-developed cutaneous vascular system.

2. A deep pit is behind prootic.

3. Blood temperature is higher than sea temperature and it is believed that the blood system serves as a temperature regulator.

Family Thunnidae (e.g., Thunnus (Tunies or Tunas) — widely distributed pelagic marine fishes. T. alalunga (Alafacore); T. albacares (yellow fin tuna); T. obesus (Big eye tuna); T. tonggol (Long tail tuna) are known from the west coast of India. Tuna fishery is highly developed in Lakshadweep.

Order (41) Pleuronectiformes (Heterosomata) [Flat fishes]:

1. The body is highly compressed and asym­metrical when adult, i.e., the eyes are shifted to one side (on the dorsal side of the head).

2. The underside so formed is highly non- pigmented.

3. The fins lack spines.

4. The swim bladder is generally absent.

Mainly coastal species, few entering rivers.

Family (1) Psettodidae (Psettodes):

Body oval and flat and thicker than other flat fishes; mouth large with strong teeth; dor­sal and anal fins separate from caudal fin; dor­sal fin not extending forward onto head and spiny rays present in dorsal and pelvic fins. Single family has two species only. Psettodes erumei— found in Indian ocean, Red sea and Malay Archipelago (Fig. 6.66A). P. belcheri — tropical West Africa.

Family (2) Bothidae (Left eye flounders):

Body oval and flat; eyes on the left side of body; mouth asymmetrical with teeth; preopercle free; dorsal fin originates above or in-front of eyes; caudal fin free from dorsal and anal fins; pectoral fins present; no spiny rays in fins.

20 genera with about 112 species, (e.g., Bothus, Pseudorhombus, Crossorhombus, Parabothus etc. — Indian, Pacific coast, Medi­terranean, Black sea). Chascanopsetta lugubris, Engyprosopon grandisquamis (Temminck and Schlegel, 1846) = Bothus poecilurus (Bleeker, 1852), Pseudorhombus arsius (Fig. 6.66B), P. triocellatus, P. javanicus, P. malayanus, etc. are Indian species.

Family (3) Pleuronectidae (Halibut or Right eye flounders):

Flat fishes with eyes on right side of the body; mouth asymmetrical with lower jaw more prominent than upper jaw; preopercle exposed and hind margin of the preopercle free; dorsal fins originate above or in front of the eye and extends up to the caudal fin; pec­toral and pelvic fins present.

Marine, occasionally in brackish water, rarely in freshwater; Tropial and Temperate seas; 39 genera with 93 species (Nelson 1994). (e.g., Pleuronectes (Fig. 6.66C), Marleyella, Nematops, Poecilopsetta, Samariscus, Paralichthodes, Hippoglossus, Atheresthes — Pacific, Atlantic, Indian).

Family (4) Hippoglossidae (Flounders) (e.g., Acanthopsetta (Japan, Indo-Pacific, Atlantic).

Family (5) Soleidae (Soles):

Oval, elongated and strongly compressed flat fishes; eyes on right side of the body; mouth small and asymmetrical with small teeth; preoparcle not seen, embedded in the skin; dorsal fin originates far forward of the eyes; dorsal and anal fins confluent with the caudal fin; pectoral and pelvic fins small; scales cycloid and ctenoid; straight lateral line.

Marine, sometimes enter into rivers; tropi­cal to temperate seas; 20 genera and 86 species, (e.g., Synaptura, Fig. 6.66D; Zebrias, Aesopia, Euryglossa orientalis, Solea elongata, Synaptura commersoniana, Zebrias quagga, Z. synapturoides occur in both sides of Indian coasts).

Family (6) Cynoglossidae (Tongue fishes):

Elongated, tongue shaped flat fishes with eyes on left side and body highly compressed; mouth asymmetrical; preopercle not visible, hidden beneath skin; dorsal fin develops from the frontal part of the head; dorsal and anal fins confluent with the caudal fin; pectoral fins absent, only left pelvic fin present; fins with spiny rays; scales cycloid and ctenoid; lateral lines 2-3.

Marine, sometimes enter into rivers; Tropical and subtropical seas. 3 genera and 110 species, (e.g., Cynoglossus, Paraplagusia, Symphurus etc.) — Cynoglossus arel, C. macrostomus, C. puncticeps, C. carpenteri, C. dispar (Fig. 6.66E), Paraplagusia bilineata — found along the Indian coasts.

Order (42) Icosteiformes or Malacichthyes [Rag fishes]:

1. The fishes are called Rag fishes, for having limp bodies.

2. The skeleton is poorly developed, mainly cartilaginous.

Family: Icosteidae (e.g., Icosteus, Icichthys and Acrotus — all are deep sea forms).

Order (43) Chaudhuriformes:

1. Body is eel-like.

2. No spines are present before dorsal and anal fins.

3. Both dorsal and annals are separated from the caudal.

4. Body is naked.

Family:

Chaudhuriidae (e.g., Chaudhuria — Found in the lake of Upper Myanmar).

Order (44) Mastacembeliformes (Opisthomi) [Spiny eels]:

1. They have eel-shaped bodies with a large mouth and an elongated snout.

2. They have a spiny first dorsal fin. Anal with three spines.

3. Dorsal, caudal and anal fins become continuous, sometimes a small caudal is separate.

Family:

Mastacembelidae (Freshwater forms of Tropical Africa, India, China) (e.g., Macro- gnathus aculeatus (Fig. 6.67A); Mastacembelus armatus, (Fig. 6.67B), M. panealus — found in the freshwaters of, southern Asia).

Order (45) Echeneiformes (Discocephali) [Suckerfishes]:

1. The first dorsal fin is modified into an oval adhesive disc or sucker for the attachment.

2. The rays of the first dorsal fin are separated into two, each of which is flat and forms the transverse fold of a sucking disc.

3. There are no spines in second dorsal and anal fins.

4. Air bladder is absent.

5. Scales are cycloid.

Family: Echeneidae (Suckerfishes):

Elongated, fusiform body with transversly laminated cephalic disc; operculum without spines; lower jaw projecting beyond the upper; dorsal and anal fins long and without spines; dorsal rays from 18-45 and anal fin from 18-41 rays; pectoral fins pointed or round with 18-32 rays; swim bladder absent; scales small and cycloid.

Marine, Indo-Pacific; 4 genera and 11 species, (e.g., Echeneis naucrates (Fig. 6.49B), Remora remora, R. brachyptera — found along the Indian coasts); Phtheirichthys, Remorina — Indian, Atlantic and Pacific coasts). Some sucker fishes have a great preference toward certain hosts. Remora australis, the whale sucker, remains attached to whales. R. osteochir is always found to be attached to spearfishes, particularly the sailfish and white marlin.

Order (46) Tetrodontiformes (Plectognathi) [Triggerfishes, globefishes, trunkfishes and molas]:

Nelson (1994) used the term ‘Tetraodontiformes’ and Munro (1982) used the term ‘Tetradontiformes’.

1. The Pelvic fins are small or absent and the dorsal fin is without spines.

2. The gill-openings are small.

3. The teeth are compressed and are partia­lly or fully fused to the upper jaw.

4. The scales are highly modified into bony scutes or reduced to spiny structures and in some lost together.

Family 1. Triacanthidae:

Small, compressed body; mouth small and terminal; jaws with molariform teeth; dorsal fin with 5 spines at the anterior part and 19-26 rays at the posterior part; anal fin with 13-22 rays; pelvic fin with a large spine; caudal fin forked.

Marine, Indo-Pacific; 4 genera and 7 spe­cies (e.g., Triacanthus = Tricanthus (Tripodfish).

Family 2. Balistidae (Triggerfish):

Body deep laterally compressed encased of a heavy armour; mouth terminal; Teeth pointed; three prominent dorsal spines; all soft fins with branched rays; scales in regular series.

Marine; Indo-Pacific and Atlantic; 11 genera and 40 species, (e.g., Abalistes stelatus, Fig. 6.68A) — starry triggerfish; Balistes (Fig. 6.68B), etc.

Family 3. Ostraciidae (Trunkfish):

Small body and encased in a bony cara­pace; hexagonal in 4 shape and sutured to one another; small, termal mouth with fleshy lips; pelvic fine absent; anal fins with 9-13 rays; upon jaw protractile.

Marine, Indo-Pacific and Atlantic; 14 gene­ra and 30 species, (e.g., Ostracion cornutum (Cowfish) (Fig. 6.68C); O. gibbossus (Trunkfish).

Family 4. Tetrodontidae (Puffers):

Small to moderate sized body and can be inflatable by air; head large and blunt; body naked short prickles; 4 fused teeth in the jaws; caudal and anal fins in the posterior part of the body with 7-15 rays; no pelvic fins; caudal fin truncate or rounded. Marine, sometimes brackish and fresh­water. (e.g., Tetraodon (Fig. 6.68D), Legocephalus lunaris, Torquigener oblongus — Puffer, globe or toadfish — warmer waters).

Family 5. Diodontidae (Porcupine fish):

Small to medium sized body, covered by well-developed sharp spines; body inflatable; mouth large and two teeth fused to form a beak­like structure; dorsal and anal fins without spines; no pelvic fins; no normal scales, (e.g., Diodon hystrix) (Fig. 6.68E).

Family 6. Molidae (Molas):

Body short and deep or oblong, markedly compressed; two fused teeth in jaws; no spine in dorsal and anal fins; no caudal peduncle; dorsal and anal fins triangular; gill openings pore- like.

Marine, Indo-Pacific and Atlantic, (e.g., Mola mola) (Fig. 6.68F) — Indo-Pacific.

Family 7. Monacanthidae (Filefishes, leather jackets):

Small to medum sized fishes; highly com­pressed bodies; dorsal fin with two spines, first large, second very small; pelvic fin rudimenta­ry; fever and less massive teeth in jaws; skin shagreen-like; second dorsal and anal fins large, more or less touch the caudal fin; caudal fin round-shape.

Marine, Indo-Pacific and Atlantic oceans. About 30 genera and 94 species.

Monacantus, Paramonacanthus, Aluterus, Navodon etc.

Order (47) Gobiesociformes (Xenopterygii) [Clingfishes and skittle fishes]:

1. The fishes are small, with a small terminal mouth and a projectile upper jaw.

2. The eyes are on the top of the head.

3. Dorsal and anal fins are opposite each other.

4. The body is naked and there is no air bladder.

5. A sucking disc is present under anterior part of body.

Family Gobiesocidae (e.g., Cobiesox Fig. 6.69A), Caularchus, Lepadogaster— warmer seas).

Order (48) Batrachoidiformes (Haplodoci) [Toadfishes and Midshipmen]:

1. They have a wide mouth and depressed head.

2. There is an undivided post temporal bone in the skull and the gill-arches are reduced to three.

Family Batrachoididae (e.g., Opsanus tau, Fig. 6.69B) (Toad or Oysterfish) — Atlantic coast of N. America); Batrachoides (Indo-Pacific).

Order (49) Lophiiformes (Pediculati) [Anglers and frogfishes]:

1. Body globose or depressed.

2. The dorsal fin is modified into an elonga­ted organ -and at its tip is a flap of skin which is used to attract the prey.

3. The pectorals are modified so that they can use to push the fishes along the sea bottom.

4. Swim-bladder when present physoclistous.

Family (1) Lophiidae (Angiters):

Head and anterior part of body much depressed and broad; body gradually soiles; mouth very large bearing large sharp teeth in the jaws; two separated dorsal fins, first with 2-3 isolated largi spines; anal fin 6-11 rays and caudal fin with 8 rays; lateral line not usually visible; gill-openings at the base of pectoral fins; pectoral fins flashy filament-like.

Marine, Indo-Pacific, Atlantic and Arctic; 4 genera and 24 species, (e.g., Lophius).

Family (2) Antennariidae (Frogfishes):

Short, globose and slightly compressed body; mouth large oblique with small teeth; small gill-openings open behind the pectoral base; 1st dorsal spine modified as a lure. 2nd and 3rd dorsal fin spines free; pectoral fin base lobate, leg-like; skin naked or spinulose. Marine, tropical and subtropical seas; 14 genera and 40 species, (e.g., Antenarius lepro­sus, Fig. 6.69C).

Order (50) Pegasiformes (Hypostomides) [Dragon fishes or sea moths]:

1. Body is encased in bony rings, a long flattened rostrum.

2. The dorsal fins are small and without spines.

3. Pectoral fins are very large.

Family Pegasidae:

Body broad and depressed, emersed in bony plates; mouth beneath, with a long’ flattened rostrum; dorsal and anal fins short; pectoral fin large wing-like with 9-19 un-branched rays; caudal fin with 8 un-branched rays.

Marine, tropical and subtropical, 2 gene­ra, 5 species, e.g., Pegasus volitans and P. dra­conis (Fig. 6.69D) — Indo-Pacific).

A.S. Romer’s (1962, 3rd ed.) classi­fication on gnathostome fishes is given below:

Class 1. Placodermi [Ck. plaks = a flat plate; derma = skin] (Silurian — Permian):

The earliest known jawed vertebrates are represented by a group of fossil fishes called placoderms which appeared during the Slurian period. These fossil fishes exhibit many structural peculiarities and are included under the class Placodermi or Aphetohyoidea.

The placoderms present wide range of adaptive radiation and flourished well in the Devonian and Carboniferous periods, but all of them became extinct by the end of Permian. The placoderms possess many pecu­liar and specialised characteristics and are regarded as the progenitors of the modern fishes. Although the placoderms form a heterogeneous group of fishes, the following features characterize the class.

The characte­ristic features are:

1. The body is protected by heavy bony armour, a feature which has given the name ‘placodermi’ to the group.

2. The hyoid arch is unspecialized and does not take part in jaw suspension.

3. The jaws are attached with the skull by their own processes. This peculiar type of jaw attachment is called autostylic. This is also called aphetohyoidean condition; because of this characteristic the placo­derms are also called Aphetohyoidea. Such type of jaw attachment is regarded as the most primitive type of jaw attachment and is regarded as the most primitive type of jaw suspension.

4. The spiracle is typically a gill-slit which is present anterior to the unmodified hyoid arch.

5. The paired fins are usually present.

The class Placodermi includes 5 orders.

They are:

(i) Acanthodii,

(ii) Arthrodira,

(iii) Antiarchi,

(iv) Macropetalichthyida and

(v) Stegoselachii.

Class 2. Chondrichthyes (Gk. chondros = cartilage, ichthys = fish):

Class Chondrichthyes is characterised by the following characters:

1. The endoskeleton is formed of cartilages. Recently the bony structure of the verte­bra has been reported in a shark.

2. Presence of placoid scales or tooth-like dermal denticles in the skin. In some, the skin is naked.

3. Absence of operculum. In holocephalans the gill openings are covered by an opercular flap.

4. Gills are of lamellar type.

5. Double nasal openings, usually single on each side.

6. Tail is usually heterocercal type (except chlamydoselachus and chimaera, where tail is of isocercal type).

7. Mouth ventral.

8. In living forms, the sutures are absent in the skull.

9. Swim bladder is absent.

The Class Chondrichthyes is divided into two subclasses:

(i) Elasmobranchii and

(ii) Holocephali.

Subclass 1. Elasmobranchii:

1. 5-7 pairs gill openings separately open to the exterior.

2. Body is covered by placoid scales.

3. Tail is mostly heterocercal type.

4. Spiracle is present.

5. Spiral valve present in the intestine.

6. High concentration of urea and trim-ethylamine oxide (TMAO) in the blood. Little water is drunk by the marine elasmobranchs and some water enters through the gills, hence little amount of urine is formed.

7. Males with pelvic claspers (Myxopterygia).

8. Jaw suspension mostly hyostylic type.

Example:

Sharks (Scoliodon), rays {Trygon) and skates (Rhinobatus). They are mostly marine and highly predaceous. Some elasmobranchs have entered into the rivers and lakes, and live permanently there.

Some species of Carcharhinus found in the Lake Nicaragua, and in the Ganges and Zambesi. Four elasmobranch species found in the Perak River in Malayasia, though they are not permanent resident but enter regularly from the sea. The Amazon sting ray, Potamotrygon is a permanent resident in the Amazon.

The subclass Elasmobranchii is divided into 3 orders:

(i) Cladoselachii,

(ii) Selachii and

(iii) Batoidea.

Order 1. Cladoselachii (Gk. klados = branch, selakhe = a shark):

1. They were abundant in the Carboniferous period.

2. The elongated body possessed terminal mouth.

3. Presence of two dorsal fins.

4. The large pectoral fins had broad bases.

5. The caudal fin is nearly symmetrical exter­nally.

6. The teeth were cladodont (branched tooth) type.

7. They had no anal fin.

They were predaceous, marine shark-like fishes.

Example:

Cladoselache.

Order 2. Selachii (Gk. Selakhe = a shark):

The living sharks and rays are included under the order Selachii.

1. The body is fusiform or elongated body.

2. Mostly cartilaginous endoskeleton.

3. Tail is heterocercal type.

4. Presence of external gill-slits.

5. First gill-slit is reduced and forms a small opening called spiracle.

6. Males with clasper.

Example : Sharks (Scoliodon, Squalus etc.)

Order 3. Batoidea:

1. The body is dorsoventraliy flattened.

2. Gill-openings ventrally placed.

3. Anterior margin of pectoral fin is fused with sides of the body or head.

4. No anal fin.

5. Dorsal fin if present placed from behind.

6. Tail is heterocercal.

Example Rays (Dasyatis), Skates (Rhinobatos).

Subclass 2. Holocephali:

1. 4 pairs gill-openings are protected by fleshy operculum.

2. Body is naked but cephalic claspers retain placoid scales.

3. Tail is absent in the adult but is present in the young.

4. Spiracle is absent in the adult but is pre­sent in the young.

5. Spiral valve is absent.

6. Jaw suspension is holostylic type.

The subclass Holocephali is divided into two orders:

(i) Bradyodonti and

(ii) Chimaerae.

Order 1. Bradyodonti:

1. Palaeozoic extinct forms, recorded in Upper Devonian.

2. The group is mainly represented by tooth plates.

3. The teeth are simple with broad, flat crowns.

4. The teeth are replaced very slowly than elasmobranchs.

Example: Bradyodontus.

Order 2. Chimaerae:

1. Presence of crushing tooth plates.

2. Absence of true centra.

3. Presence of persistent notochord surroun­ded by partly calcified rings.

4. Palatoquadrate is fused to the neurocranium (holostylic).

Example:

Ratfish (Chimaera), Elephant- fish (Callorhynchus).

Class 3. Osteichthyes (Gk. osteon = bone, ichthys = a fish):

The characteristic features are:

1. The skeleton is partly or largely formed of bony structures.

2. Body covered by dermal ganoid, cycloid or ctenoid scales.

3. Gills remain in a pouch, covered by a bony operculum.

4. Gills are of filamentous type.

5. Tail is mainly homocercal type.

6. Swim bladder is present in most forms except benthic feeders and deep sea forms.

7. Mouth terminal.

8. Clasper is absent in males.

9. Spiracle is absent except in some primitive forms (Acipenser and Polypterus).

The class Osteichthyes is divided into two subclasses:

(i) Actinoptrygii and (ii) Sarcopterygii.

Subclass 1. Actinopterygii (Ray finned fishes):

The characteristic features are:

1. The fins are membranous, supported by jointed radiating rays.

2. Internal nostrils are absent.

3. Palatoquadrate are not fused with cranium.

The subclass is divided into 3 superorders:

(i) Chondrostei,

(ii) Holostei and

(iii) Teleostei.

Superorder 1. Chondrostei (Gk. chondros = cartilage, osteon = bone):

1. Internal skeleton is mainly cartilaginous but little bone present.

2. Heterocercal tail.

3. Spiral valve in the intestine.

4. Scales are covered by a layer of ganoin.

5. Spiracle present (absent in Scaphirhynchus).

Example:

Bichir (Polypterus), Sturgeon (Acipenser), Shovel-nosed sturgeon (Scaphi- rhynchus), Paddlefish (Polyodon).

Superorder 2. Holostei (Gk. holos = whole, osteon = bone):

1. Internal skeleton bony.

2. Abbreviated heterocercal tail but rounded in outline in Amia and not subdivided in Lepisosteus.

3. Body covered with cycloid scales in Amia and rhomboid scales in Lepisosteus. Generally the scales have lost their shiny ganoid covering.

4. Gape of the mouth small.

5. Spiracle absent.

Example:

Bowfin (Amia), Garpike (Lepisosteus).

The actinopterygians gradually invaded the oceans in the Jurassic Period but oceanic holosteans became rare in the Cretaceous period and at present two surviving genera are found in the freshwater.

Superorder 3. Teleostei:

1. Body covered with thin cycloid or ctenoid scales.

2. Homocercal tail.

3. Small paired fins.

4. Large maxilla which takes part in the formation of upper jaw.

5. Spiracle is absent.

The members of the teleosteans originated in the oceans but later invaded freshwater environment (Romer, 1962).

Example:

Rest of the living species. Some examples are Rohu (Labeo), Katla(Catla), Eel (Anguilla), etc.

Subclass 2. Sarcopterygii (Gk. sarkos = flesh, pterygion = fin):

1. Scales are of cosmoid type.

2. Internal nostrils are present in some groups.

3. Fleshy lobed paired fins are present.

4. Intestine with spiral valve.

It consists of two orders:

(i) Crossopterygii and

(ii) Dipnoi.

Order 1. Crossopterygii:

1. Body covered with large cycloid scales with enamelled surface.

2. The tail is diphycercal with a median lobe.

3. Presence of two dorsal fins of which the posterior one has a fleshy lobe. The paired fins have also fleshy lobes.

4. Presence of an internal nostril (Choana).

5. Teeth with labyrinthine structure.

6. Respiration is performed by gills.

7. Swim-bladder is highly reduced and is neither hydrostatic nor a respiratory organ.

Example: Coelacanth (Latimeria)

Order 2. Dipnoi:

1. Body is covered by thin, large cycloid scales.

2. Isocercal or proto-cercal type of caudal fin.

3. Presence of two internal nostrils.

4. Single dorsal fin which is continuous with the caudal fin.

5. Paired fins with basal fleshy structures.

6. Swim-bladder is modified into lung which is used in respiration.

7. Small denticles are fused to form crushing tooth-plates.

8. Dermal bones on the skull.

Example:

Lung fishes (Protopterus (Africa), Lepidosiren (S. America) and Neoceratodus (Australia).