Optimization of inclusion level of protein in larval diet of Labeo rohita (Hamilton, 1822) during early ontogeny.

Optimization of larval feed is a prerequisite for the successful ontogeny of fish larvae. A feeding trial of 35 days was conducted in a replica of five (500 larvae per tank/2500 per group), to determine the dietary protein requirements of rohu Labeo rohita larvae. Four experimental nano-particulate diets (P45, P50, P55, P60) having 45, 50, 55, and 60% CP were prepared and fed to L. rohita larvae from 3 to 35 DAH (days after hatching). Sampling for growth assessment, digestive enzymes, and gene expression study was done on 3, 10, 15, 20, 25, 30, and 35 DAH. Among all the diets, P55 followed by P60 showed the most significant positive effect on growth (NWG, SGR) and survival of fish larvae. Amylase did not show any significant change among the experimental groups; however, total protease, trypsin, and chymotrypsin showed significantly high activity in P55, followed by P60, and the least activity in P45. Moreover, a positive correlation was observed between age DAH and GH and IGF-1 in all groups, while a negative correlation was observed with myogenic-regulating factors MRFs, i.e., MyoD and MYF-5. The significantly higher expression of GH and IGF-1, and a sustained higher expression of MRFs in P55 among all the studied groups, indicate 55%CP as the optimum dietary protein requirement for L. rohita larvae.