Dietary protein requirement of giant mud crab Scylla serrata juveniles fed iso-energetic formulated diets having graded protein levels

The protein requirement of juvenile mud crab Scylla serrata (body weight - 50.25 +/- 0.051 g, carapace width = 59.3 +/- 0.04 mm) fed with different iso-energetic, iso-lipidic diets with graded protein levels (15-55% crude protein at 5% intervals) was determined. The feeding trial was conducted for a period of 63 days to determine the minimum and optimum protein requirement of juvenile S. serrata. The crabs fed with 15% and 20% dietary protein levels showed 100% and 12.5% of mortalities respectively. The mortalities observed in the above treatments were associated with the prolonged intermoult duration (46 and 32 days respectively). All other treatments recorded 100% survival. The best growth performance as well as the nutrient turn-over was recorded in crabs fed with 45% crude protein in the diet. Second-order polynomial regression of specific growth rate (SGR) as well as body protein gain vs. dietary protein levels suggested that 46.9-47.03% dietary protein is required for the best growth response and protein deposition in juvenile S. serrata. An extrapolation of 'SGR' and 'daily protein gain' upon the 'dietary protein level' axis (Y = 0) showed that 14.7-16.2% dietary protein is necessary for the minimum maintenance metabolism.