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

Abstract 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%.