Effects of Varying Dietary Protein Level on Growth, Nutrient Utilization and Body Composition of Juvenile Blackfin Sea Bream, Acanthopagrus berda (Forsskal, 1775)

The optimum dietary protein requirement of juvenile blackfin sea bream, Acanthopagrus berda (live body weight 8.1-89.2 g) was investigated. Fish juvenile were collected from Sonari Channel Hawks bay and were maintained in recirculating water system (rearing glass aquaria of 120 lit, water temperature 25C). Four isoenergetic (20.1 kJ/g digestible energy) diets were formulated to contain protein levels of 20%, 30%, 40% and 50%, and fed one of the experimental diets at a daily ration of 2% body weight for 90 days. Higher weight gain and growth rate were observed in the fish fed with 40% and 50% protein diets. Broken line regression analysis generated an optimum protein levels of 42.0% for blackfin sea bream. Fish whole body composition showed that lipid content of the fish fed with 40% and 50% was lower and moister content was higher. The hepatosomatic index (HSI) of the fish fed with 40% and 50% was greater than that of the fish fed with 20%-30% protein level. No significant difference was observed in protein and ash contents of whole fish for the diets of 20% to 50% protein. Fish fed 40% and 50% protein diets showed higher nitrogen gain and nitrogen retention efficiency than those fed on other diets. These results suggest that under similar culture conditions, the optimum protein level of the juvenile sea bream (from initial weight of 8.1 g to 89.2 g) is 42.0%.