The nutrient requirements of most Indian major carps are incompletely documented. This is because most cyprinids are cultured either extensively or semi-intensively, and are rarely fed formulated commercial feeds. Most of the investigations on the nutrient requirements of Indian major carps including mrigal, have been carried out on fry and fingerlings and there is considerable variation in the results. Some of the variation can be attributed to biological differences such as fish size, age, temperature, while the remainder are a consequence of different experimental procedures and protocols. The optimum dietary protein requirement for maximum growth is dependent on protein quality and fish size and ranges from 40 to 45 percent for mrigal fry and 30 to 45 percent for fingerlings (Mohanty, Swamy and Tripathi,1990; Singh et al., 1987; Swamy et al., 1988; Das and Ray, 1991; De Silva and Gunasekera, 1991). Kalla, Bhatnagar and Garg (2004) suggested that mrigal fry and fingerlings be fed on supplementary diets containing about 40 percent protein, preferably of plant origin. Hassan et al. (1995) and Hassan and Jafri (1996) also recorded optimal growth and feed conversion of mrigal fry and fingerlings with a 40 percent CP diet, P:E ratio of around 8.9 kcal/g and an energy content of 15.09 kJ/g, although maximum protein utilization and conversion occurred at a similar energy content but a lower protein content (30 percent CP) in the diet (P:E ratio of 12.1 kcal/g). Mrigal requires the same ten essential amino acids as other finfish. The essential amino acid requirement of mrigal fingerlings and juveniles are reasonably well established and are summarized in Table 2. Most of these values were determined under controlled laboratory conditions and may not be applicable under farming conditions. No information is available on the dietary protein requirements of mrigal broodstock.
The optimum dietary lipid level for mrigal fry and fingerlings is between 5 and 9 percent (Singh and Sinha, 1981; Singh, 1983; Jafri et al., 1995; Marimuthu and Sukumaran, 2001) and the optimum CHO:L ratio is reported to be 3.4:1.0 (Erfanullah and Jafri, 1998).
The dietary fatty acid requirements of cultured cyprinids are not well known. Work by Takeuchi and Watanabe (1977) demonstrated that common carp require equal amounts of dietary linoleic acid (18:2n-6) and linolenic acid (18:3n-3). The dietary phospholipid requirement of Indian major carp (including mrigal) larvae was estimated to be 4 percent (Paul et al., 1998).
The optimum carbohydrate requirement of mrigal fingerlings was found to be 28 percent (Singh and Sinha, 1981). Although all Indian cyprinid species appear to be capable of utilizing carbohydrates fairly well, the findings of Erfanullah and Jafri (1998) suggested that mrigal might not tolerate the carbohydrate levels suggested for catla and rohu.
Indian major carps obtain their vitamin requirements mainly from natural food in ponds. Based on weight gain, mortality, behavioural and morphological criteria the optimum vitamin C requirement for newly hatched mrigal is between 650 and 700 mg/kg diet (Mahajan and Agrawal, 1980) and the dietary vitamin E requirement of mrigal fry is 99 mg/kg dry diet (Paul, Sarkar and Mohanty, 2004a).
Based on growth performance, FCR, carcass phosphorous retention, Paul et al. (2004b) recommendded an optimum Ca:P ratio of 0.19:0.75 for mrigal fingerlings and Saxena and Talwar (1996) reported an optimum dietary potassium level of 0.41 percent. Sen and Chatterjee (1979) reported that cobalt chloride and manganese at a rate of 0.01 mg/day/fish results in higher growth and survival rates in Indian major carp larvae, fry and fingerlings. In general, carps appear to be less sensitive to mineral deficient diets than other fish. This is possibly due to their obtaining the required minerals from natural sources under pond culture condition.
