INTRODUCTION: The mrigal (Cirrhinus cirrhosus) is the most widely farmed species among the Indian major carps of the Indo-Gangetic floodplains of Bangladesh, India and Pakistan. It also found in the rivers of Myanmar that drain into the Bay of Bengal. It is an important component of carp polyculture throughout South Asia. It was introduced for aquaculture, together with catla (Catla catla) and rohu (Labeo rohita), to other areas of India beyond its natural range in the early 1940's and in the 1950's and 1960's to other Asian countries (Jhingran 1982). SCIENTIFIC NAME: Cirrhinus cirrhosus (Bloch, 1795), formerly Cirrhinus mrigala (Hamilton, 1822) DISTRIBUTION: Naturally distributed in south Asian countries (Bangladesh, Cambodia, India, Laos, Malaysia, Mauritius, Myanmar, Nepal, Pakistan, Sri Lanka and Vietnam). HABITS: Inhabit in tropics, hardy, can tolerate low oxygen conditions and salinity levels up to 5 ppt; minimum tolerable temperature 14ºC; reproduces between 27 - 31ºC. adults are almost entirely herbivorous, feed on plankton, but also graze on algae and detritus. Spawning occurs in marginal areas of the water body with a depth of 50-100 cm over a sand or clay substrate. SPAWNING: Mrigal attain first maturity when about two years old (800 - 1,200 g) and spawn during June to August. In hatcheries, the same fish can spawn two to three times, early in the season. They lose condition towards the end of the season. Spawning occurs in marginal areas of the water body with a depth of 50-100 cm over a sand or clay substrate The fecundity of mrigal ranges from 100,000 to 200,000 eggs/kg body weight (Jhingran and Khan 1979). For induced spawning, two injections of crude carp pituitary gland (2-3 mg and 5-8 mg/kg) are given to a female at an interval of 4-6 hrs, as against only one (2-3 mg/kg) to males at the time of the second injection to the female. a female and two males in a running water spawning task should then spawn within six hours. If spawning has not taken place, the female is stripped and the eggs fertilized with semen stripped from males. The fertilized eggs hatch after 18-24 hrs depending upon the water temperature. Optimum temperature for spawning and hatching is 280C (Chaudhuri 1963). Jhingran and Pullin (1988) have reviewed the use of materials other than carp pituitary, for induced spawning. GROWTH: Nursery: Nursery ponds are prepared by liming and fertilization with cover or poultry manure, to produce zooplankton (especially rotifers and small cladocerans). Before stocking the nursery ponds the predators of post-larvae, especially copepods and insects, are controlled with appropriate chemicals (Jhingran and Pullin 1988). Post-larvae are stocked at 5 million/ha and are given supplementary feed in the form of a fine powder comprising a 1:1 mixture of groundnut/mustard oil cake and rice or wheat bran. This is given daily at two, three and four times the weight of post-larvae stocked, increasing the ration at five days intervals. The post-larvae grow to about 25 mm in 15 days, with survival around 70%. Grow-out: The fry are raised in larger rearing ponds which are fertilized in a similar manner to nursery ponds and then normally stocked as part of a combination of catla, rohu and mrigal. The total stocking rate in rearing ponds is usually around 100,00 - 125,000 fry/ha, of which 30-40% are mrigal. Mrigal is a bottom feeder and consumes mainly detritus and decayed vegetation, along with some plankton (20-25%). Growout ponds (0.2 - 5.0 ha) are stocked with mrigal fingerlings at 10-35% of the total stocking density density depending upon the species mix. In polyculture of Indian major carps (catla, rohu and mrigal), mrigal are normally 30-40% of the population but this is reduced to 10-15% when common carp are included. Growout ponds are also prepared initially by liming and fertilization with periodic fertilization (organic and inorganic) thereafter. Mrigal normally registers better growth than rohu in ponds that have rich bottom feeding or when supplementary feed is provided regularly. In sewage-fed ponds, mrigal attain a weight of about 1 kg in 6 months. USES: Mrigal is a tasty fish, despite its fine bones. It has a good market wherever it is farmed or fished. It is marketed either fresh or packed with ice. Mrigal will continue to be a very important species in carp polyculture in Asia. Monoculture of mrigal is not known at present, but the availability of improved genetic material (such as that being developed in Vietnam) may lead to the development of cage, pen, running water, and closed recirculatory systems, using mrigal alone. Mrigal is also a good fish for sewage-fed ponds, where the abundance of natural food almost high density stocking. REFERENCES:
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