Growth and feed utilization of hatchery-reared juvenile Nassau grouper fed four practical diets.
Effects of 4 practical diets (for carnivorous marine fish), on growth, feed utilization and body composition of hatchery-reared juvenile Nassau grouper, Epinephelus striatus, (mean weight±SD = 2.37±0.75 g) were compared for 56 days in 145-litre flow-through seawater (36-38 ppt) aquaria. Diets differed in CP and crude lipid (CL) content as follows: low-CP (43.5%), low-CL (5.91%) trout grower (LP-LL); mid-level CP (52.7%), high-CL (15.2%) salmon grower (MP-HL); mid-level CP (55.6%), low-CL (7.79%) Japanese formulation for carnivorous fish (MP-LL) and a high-CP (61.8%), high-CL (14.2%) research diet for dolphin (mahimahi), Coryphaena hippurus, (HP-HL). Energy to protein ratios (E:P) of these diets were 35.2, 32.0, 28.3 and 28.9 kJ/g, respectively. Relative growth rate (RGR, percent increase in weight) and specific growth rate (SGR, percent increase in body weight daily) were strongly correlated (P<0.0005) to dietary CP and E:P ratio and were higher (P<0.05) for fish fed on MP-LL and HP-HL diets (RGR = 454-502%; SGR = 3.05-3.19% daily) than in the LP-LL and MP-HL diets (RGR = 68.6-160%; SGR = 0.93-1.71%). Feed utilization, including feed conversion ratio, protein efficiency ratio, apparent net protein retention, and apparent NE retention were also highly correlated (P<0.0005) to dietary CP and E:P ratio. These parameters were higher (P<0.05) in the MP-LL diet than in the other diets. No clear relationship between dietary nutrient levels and proximate body composition was observed. Results indicate that cultured juvenile Nassau grouper require a dietary protein level above 55% and an E:P ratio below 28.9 kJ/g for optimum growth.