Mrigal - Cirrhinus mrigala

(Hamilton, 1822) [Cyprinidae]

Taxonomic and biological features:

Distinguishing characters
Body elongate with depressed and obtusely rounded snout (Figures 1 and 2). Scales large and cycloid. Lateral line continuous to centre of caudal fin base (Figure 1). Abdomen rounded, body depth and head length nearly equal. Mouth terminal and wide, lips without fringe, upper lip not continuous with lower lip.  Lower lip sharp with a knob at the mandibular symphysis. Mouth with single pair of short rostral barbels (Figure 3). Dorsal fin with 15-17 soft rays is slightly nearer to snout than caudal base. Pectoral fins shorter than head. Anal fin not extending to caudal fin. Pectoral, pelvic and anal fins with 18-19, 9 and 8 soft rays, respectively. Caudal fin homocercal and deeply forked. Body colour usually dark grey on the back and silvery on the sides and belly. Fins are grayish; tips of pelvic, anal and lower lobe of caudal are tinged orange, especially during the breeding season. Similar to all carp species, the mouth of mrigal is devoid of any teeth on the jaws. Pharyngeal teeth plough-shaped and arranged in rows of 5, 4, 2/2, 4, and 5.

The alimentary canal becomes functionally complete on the third day after hatching, when it is a simple, nearly straight tube. The alimentary canal remains shorter than the body length up to 7 days after hatching and thereafter increases at a much faster rate, becoming longer than the body (Kamal, 1967). In the adult stage the alimentary canal becomes coiled (Figures 4 and 5) and the gut length to body length ratio is around 15-16:1 (Das and Moitra, 1955; Das and Moitra, 1956).

In the absence of gastric glands in the intestinal bulb, the digestive function is performed by bile and pancreatic juices released in the anterior part of the intestinal bulb. The pH of in the intestinal fluid in the intestinal bulb ranges from 6.8-7.1, but decreases to within a range of 6.2 to 6.5 in the hind gut (Figure 5). Protein digestion occurs at pH 7.0 to 7.1 in the midgut. The intestine provides a large surface area for absorption (Jhingran and Khan, 1979).

Reproduction
Sexual maturity is attained within 1 or 2 years depending on location. Hanumantha Rao (1974) reported first maturity of mrigal at 349 mm, when the fish are 2 years old. Fecundity varies from 1 – 2 x 104 depending upon the size of the fish. In natural waters breeding occurs during the south-west monsoon season in shallow newly inundated wetlands and or river side pools. The fish breed in water of 0.5 to 1.0 m (Talwar and Jhingran, 1991). Hypophysation is practiced to induce spawning under captive conditions.