Optimum dietary protein and lipid specifications for juvenile malabar grouper (Epinephelus malabaricus)

An 8-week comparative slaughter experiment was carried out to determine the optimal dietary dry matter (DM) crude protein (CP) and lipid for growth and nutrient retention of malabar grouper. Fingerlings of mean (± SD) starting weight of 17 ± 1.3 g were fed twice daily to satiety one of 16 pelleted dry feeds (∼ 93% DM) that provided a 4 × 4 factorial comparison of serially incremented CP (from 44 to 60%) and lipid (from 7 to 23%) with three tank replicates (10 fish per tank). Tanks (100 L) were situated within an enclosed laboratory and provided with bio-filtered, constant temperature (29 ± 0.7 °C) recirculated seawater and with supplementary aeration.Fish survival averaged 94 ± 5.3% and was unaffected by treatment. Modelling of the fish's response to dietary CP and lipid showed that growth, feed conversion ratio (FCR) and dietary energy retention were all optimized when dietary CP was 55–56%; DM feed intake was highest for diets with the highest protein (60%) and lowest lipid (7%) content while N retention was maximized at 49% CP. The optimal dietary lipid level was about 12% for growth rate and N and energy retentions, and 17.5% for FCR. Changes in the whole body (WB) composition of the fish were more direct: protein composition decreased linearly as dietary protein increased (with increasing dietary lipid tending to have an opposing effect), while lipid composition increased linearly as dietary protein and lipid both increased. Thus, WB lipid was highest for fish fed the highest protein (60%) and the highest lipid (23%) diet while WB protein was greatest for fish fed the lower protein (44 or 50%) and highest lipid (23%) diets. Recommended dietary protein, lipid and protein to energy ratio specifications for optimal productivity of juvenile malabar grouper are 55%, 12% and 28 g CP:MJ gross energy, respectively.