Abstract:In order to investigate the optimal dietary protein and energy levels of a new juvenile hybrid grouper (Epinephelus lanceolatus♂×E. moara♀), nine diets were formulated containing three dietary protein levels (46%, 50% and 54% crude protein) and three dietary energy levels (20.00 kJ/g, 20.50 kJ/g and 21.00 kJ/g gross energy), the dietary protein-energy ratio was in the range of 22.04 to 26.87 mg/kJ. Juvenile grouper averaging (46.23±0.51) g were fed the test diets for 56 days. The results indicated that the interaction between protein and energy had a significant effect on the weight gain (WG) of grouper (P<0.05), the weight gain rate (WGR) and specific growth rate (SGR) increased with increasing of dietary protein and energy levels (P<0.05). Protein deposition rate (PDR) and hepatosomatic index (HSI) were significantly affected by the interaction between protein and energy (P<0.05). The energy retention rate (ERR) and condition factor (CF) increased with increasing of dietary protein levels (P<0.05), while the protein efficiency ratio (PER) increased first and decreased afterwards (P<0.05). The PER and ERR increased with increasing of dietary energy levels (P<0.05). PDR and PER of D6 group were significantly higher than other groups (P<0.05). The interaction of protein and energy had no significant effects on moisture, crude protein and crude ash of whole fish and muscle (P>0.05). The crude protein of whole fish and muscle increased with increasing of dietary protein levels (P>0.05). Moisture decreased with increasing of dietary energy levels (P<0.05). Crude fat of whole fish increased with decreasing of dietary protein-energy ratio (P<0.05). The interaction of protein and energy had significant effect on the activities of trypsin, lipase and amylase (P<0.05). The pepsin activity increased with increasing of dietary protein levels (P<0.05), and dietary energy levels had no significant effect on it (P>0.05). The trypsin activity of D6 group was significantly higher than other groups (P<0.05), which increased first and then decreased with decreasing of dietary protein-energy ratio (P<0.05). The lipase activity of fish fed diets containing 21.00 kJ/g energy was significantly higher than other groups (P<0.05). According to these results, a diet containing 50% protein and 21.00 kJ/g energy was recommended for efficient growth of juvenile hybrid grouper.
