The following points highlight the top five varieties of fishes. The varieties are: 1. Shark 2. Rohu 3. Singhi 4. Magur 5. Koi.
Contents
Variety # 1. Shark (Fig. 137): A Cartilaginous Fish:
Quite a different types of sharks are available in the oceans of our country, of which the most common is Scoliodon sp. This shark may attain a size of 60 to 90 cms. or 2 to 3 feet. The dorsal side of the body is dark-grey and the ventral side is white. Both ends of the body are pointed. The entire body is divisible into three regions— head, trunk, and tail. The head is slightly flattened and drawn anteriorly into a pointed snout.
Mouth is present on the ventral side of the head and is semilunar in appearance. One nostril and one eye is present on each side of the head. The eyes are prominent and provided with functionless eyelid. Near the junction of head and trunk, on each side of the head lie five small transverse openings called gill-slits.
The trunk is indistinctly separated from the head. The entire body is covered by a special type of small and pointed scales. These scales are called placoid scales. Like the cycloid and ctenoid scales, these scales do not cover the anterior part of the next row. Lateral line sense organ runs along each lateral side of the body from head to tail.
The vent or outlet of the food canal is present on the ventral side of the body. Another pair of small opening, abdominal pore is present slightly posterior to the vent. In the male scoliodon only, a pair of elongated claspers are present in this region. The body contains a number of fins with supporting fin-rays. Some fins are paired, while others are unpaired. Following fins are present in scoliodon.
A. Paired Fins:
1. Pectoral fin—one on each lateral side, triangular, present near the junction of head and trunk.
2. Pelvic fin—one on each side of the vent. In males the claspers are present close to the pelvic fin.
B. Unpaired Fins:
1. Dorsal fin:
Divided into two parts—anterior dorsal fin and posterior dorsal fin. Both these parts of the dorsal fin are triangular and the anterior is larger than posterior.
2. Ventral fin:
Present on the ventral side and posterior to the pelvic fins.
3. Caudal fin:
Divided unequally into two parts—dorsal lobe and ventral lobe. The dorsal lobe is larger than ventral lobe and contains the last part of the vertebral column. This type of tail is called Heterocircal tail.
Variety # 2. Rohu (Fig. 138): A Bonny Fish:
This is the most important edible fish of our country. It is scientifically known as Labeo rohita. It grows well in ponds and pools to attain a weight of 20-25 kg., but never breeds in enclosed water. A reddish tinge is visible throughout the body of these fishes.
The body is divided into three parts:
(1) Head,
(2) Trunk, and
(3) Tail.
The head is mere conspicuous than Bhetki. It is pointed anteriorly and is terminated by mouth. Mouth is bounded by jaws which are devoid of teeth. A pair of barbs are present near the mouth. The eyes are large and slightly reddish in colour.
The gill openings are broad and covered by strongly built operculum. The body is covered by cycloid scales. Along each lateral side runs the lateral line sense organ, which begins near the opercular opening and ends to the tail region. Following paired and impaired fins with supporting fin-rays are present.
A. Paired Fins:
1. Pectoral Fin:
One on each ventrolateral side, near the opercular opening. Each fin contains 19 fin-rays.
2. Pelvic fin:
Present on the ventral side, consists of 9 fin-rays.
B. Unpaired Fins:
1. Dorsal Fin:
Present on the mid-dorsal region of the body. Provided with 13 fin-rays.
2. Anal Fin:
Present on the mid-ventral region of the postanal part. Supported by 4-6 fin-rays.
3. Caudal Fin:
The caudal fin is divided equally into two parts. Each part is pointed at its free end. Several fin-rays are associated with the caudal fin.
Variety # 3. Singhi (Fig. 139): Air Breathing Fish:
It is scientifically known as Heteropneustes fossilis. It is a common air-breathing fish which in addition to gills possesses an air tube within its body. While living under water these fishes frequently visit the surface to breathe air. If these fishes are prevented to come near the surface, they die. It shows that mechanism of aquatic respiration alone cannot meet the oxygen requirement in these fishes.
The grey-coloured body is slender and devoid of scales. It has three distinct regions:
(1) Head,
(2) Trunk, and
(3) Tail.
The tail is the largest part of the body. The head is small, flattened and its anterior end is marked by an opening called mouth. Around the mouth are present 4 pairs of barbels, which are sensory in function. A pair of nostrils and a pair of eyes are present on the head region. Following fins with supporting fin-rays are present.
A. Paired Fins:
1. Pectoral Fin:
One on each side of the trunk near the opercular opening. Each consists of 9 fin-rays of which the first one is large, sharp and pointed. It acts as defensive organ.
2. Pelvic Fin:
Placed on the ventral side of the trunk and close to the pectoral fin. It is small and has 6 fin-rays.
B. Unpaired Fins:
1. Dorsal Fin:
Very small, placed on the mid-dorsal region of the body.
2. Anal Fin:
This is the largest fin with numerous fin-rays. Present along the entire ventral side of the tail region.
3. Caudal fin:
Round, small and is present on the posterior- most end of the tail.
Variety # 4. Magur (Fig. 140): Air Breathing Fish:
This is another air-breathing fish. Here the accessory respiratory organ is branched and placed near the gills. This fish is scientifically known as Clarius batrachxis. The head of this fish is larger than singhi and mouth is present on the ventral side. Of the eight barbels, two are much stouter and longer, while the others are similar. Following paired and impaired fins are present, which differ from the Singhi.
A. Paired Fins:
1. Pectoral Fin:
Present near the opercular opening, first fin- ray is modified into a sharp defensive structure.
2. Pelvic Fin:
Present on the ventral side and close to the pectoral fin. Supported by soft fin-rays.
B. Unpaired Fins:
1. Dorsal Fin:
Very large, extends along the mid-dorsal line of entire trunk and tail region. Supported by innumerable soft fin-rays.
2. Anal fin:
Present along the mid-ventral line of the tail region. Numerous soft fin-rays are present.
3. Caudal Fin:
Semicircular and present on the terminal end of the tail region.
Variety # 5. Koi (Fig. 141): Air Breathing Fish:
It is scientifically known as Anabus testudineus. It possesses fan-shaped accessory respiratory organ near the gills. These are small fishes (15 to 20 cms. in length) with flattened body; the dorsal side is slightly curved. The head is prominent, triangular and terminated by a broad mouth.
Eyes are paired and quite prominent. The body is covered by rows of ctenoid scales and along each side of the body runs the lateral line sense organ. The line is breached near the tail region. Following paired and impaired fins are present, where the supporting fin-rays are all sharp and pointed.
A. Paired Fins:
1. Pectoral Fin:
Placed near the opercular opening. The free end of the fin is broad and semicircular, while the base is narrow.
2. Pelvic Fin:
Placed mid-ventrally and close to the pectoral fin.
B. Unpaired Fins:
Dorsal Fin:
Consists of two parts—anterior elongated part supported by stiff fin-rays and posterior round part supported by soft fin-rays.
Ventral Fin:
Like the dorsal fin, consists of two parts— anterior elongated part which is supported by stiff fin-rays, and posterior round part supported by soft fin-rays.
Caudal Fin:
Round, short and supported by numerous fin rays.