Optimum dietary protein level and protein to energy ratio for growth of grouper (Epinephelus malabaricus)

A series of two experiments was conducted to study the optimum dietary protein level and protein to energy ratio of juvenile groupers. In Experiment 1, eight isoenergetic fish meal based semi-purified diets ranging from 0 to 56% protein in 8% increments were fed for 8 weeks to triplicate groups of grouper (initial weight: 9.22 +/- 0.11 g per fish). Weight gain of fish was proportional to the protein content of the diet up to an incorporation rate of 48%. Feed efficiency (FE) increased with increasing dietary protein level, and the diet with 48% protein yielded the lowest FE. Fish fed the 56% protein diet had the highest body protein and lipid contents, and the lowest body moisture content. The dietary protein level that yielded maximum growth was 50.2% based on a broken-line model estimation of weight gain. In Experiment 2, two dietary protein levels (50% and 44%) were used along with four energy levels at each protein level (305, 340, 375 and 410 kcal per 100 g diet). The experimental diets were fed for 8 weeks to triplicate groups of grouper (initial weight: 10.70 +/- 0.14 g per fish), Weight gain of fish was not significantly (P > 0.05) different at 50% dietary protein regardless of energy level. However, the 44% protein diet at energy levels of 340 and 375 kcal per 100 g improved weight gain of fish. Fish fed the 44% protein with 340 or 410 kcal per 100 g diet had higher body lipid content. These data suggest that when the energy level of the diet is maintained at 340-375 kcal per 100 g, the dietary protein level for juvenile grouper can be lowered from 50% to 44%.