Effects of dietary lipid and energy to protein ratio on growth and feed utilization of juvenile mutton snapper Lutjanus analis fed isonitrogenous diets at two temperatures

Growth and feed utilization of juvenile, hatchery-reared mutton snapper Lut janus analis (mean weight = 12.2 g) were compared for 40 d in laboratory aq uaria on four isonitrogenous diets (45% crude protein) of varying lipid con tent (6, 9, 12 and 15%) with energy:protein ratios (E : P; kJ/g protein) of 33.9, 36.3, 38.8, and 41.2, respectively. Growth on these diets was compar ed under temperatures of 25 and 30 C. Final weights (Wt(f)) and specific gr owth rates (SGR) were higher (P < 0.05) at lower dietary E:P ratios of 33.9 and 36.3 (Wt(f) = 20.3-22.0 g; SGR = 1.25-1.35%/d) than at E:P ratios of 3 8.8 and 41.2 (Wt(f) = 17.2-17.7 g; SGR = 0.84-0.85%/d). Growth at 30 C (Wt( f) = 21.5 g, SGR = 1.35%/d) was higher (P ( 0.05) than at 25 C (Wt(f) = 17. 3 g; SGR = 0.82%/d), Feed consumption (FC) was higher (P < 0.05) at a dieta ry E:P ratio of 33.9 (1.57%/d) than at 36.3 (1.27%/d) or 38.8-41.2 (0.89-0. 98%/d), Growth was highly correlated (P < 0.01) to E:P ratio and to feed co nsumption. Feed conversion ratio (FCR = 2.17-3.98), protein efficiency rati o (PER = 0.58-1.03) and apparent net protein retention (ANPR = 15.8-20.0%) were not significantly (P > 0.05) affected by dietary E : P ratio. Apparent net energy retention (ANER) was higher (P < 0.05) at E:P ratios of 33.9 an d 36.3 (9.50-9.98%) than at E:P ratios of 38.8 and 41.2 (7.15-7.10%). Feed utilization parameters were significantly (P < 0.05) better at 30 C (FC = 1 .36%/d; FCR = 2.6; PER = 0.88: ANER = 10.2%) than at 25 C (FC = 1.03%/d; FC R = 3.38; PER = 0.69; ANER = 6.72%), with the exception of ANPR (17.0-17.8% ). Maximum growth and energy retention in juvenile mutton snapper using a d iet containing 45% crude protein was obtained at dietary lipid levels of 6- 9% and E:P ratios of 33.9-36.3 kJ/g protein. Studies which determine optimu m protein levels and the effects of reducing E:P ratios below 33.9 kJ/g are needed to improve feed conversion and growth.