Effect of Dietary Protein and Energy Levels on the Growth and Body Composition of Juvenile Orange-spotted Grouper, Epinephelus coioides

To evaluate the protein and energy requirement of orange-spotted grouper, Epinephelus coioides fingerlings, nine experimental diets including 3 levels of crude protein (40%, 50% and 60%) and 3 levels of digestible energy (DE, 14, 16 and 18KJ.g-1), were tested. Triplicate 300 L circular tanks provided with flow-through water system (2L. min-1) and air stone and each stocked with 20 juvenile of grouper fish (16.79±0.4g) were applied to adopt an experimental test for 8-weeks rearing period. The stocked fishes were fed experimental diets to approximate satiation, twice a day. Results showed that the survival rate, hepatosomatic index (HSI) and condition factor (CF) were independent of the dietary treatments, but final weight, weight gain, specific growth rate(SGR), feed efficiency (FE), feed conversion ratio (FCR), protein efficiency ratio (PER) and daily feed intake (DFI) were significantly affected by protein and digestible energy levels (P<0.05). Diet 5 (50%CP and 16KJ.g-1 DE) was the preferred among the tested diets and resulted in the best growth performance, feed and protein efficiency and nutrient utilization among the examined diets. DFI was the lowest for diet with the highest protein (60%) and energy (18KJ.g-1). Apparent net protein utilization (ANPU) varied insignificantly (P>0.05) between the treatments. viscerosomatic index(VSI) increased significantly with the increasing of diet energy level. Body lipid, ash and moisture contents were affected by dietary protein and energy levels. Body lipid content increased with increasing dietary energy levels, but carcass ash and moisture decreased. Body protein content was not affected by dietary energy level, but significantly increased when protein increased from 40% to 50% at same energy levels (P<0.05). The study revealed that fingerlings of orange-spotted grouper, E. coioides showed highest growth performance when fed diet containing 50% crude protein, 16KJ.g-1 digestible energy with the P/DE ratio, of 31.25mg/kJ.