Effects of dietary protein and lipid levels with different protein-to-energy ratios on growth performance, feed utilization and body composition of juvenile red-spotted grouper, Epinephelus akaara

An 8-week feeding trial was conducted to assess dietary protein and lipid levels on growth performance, feed utilization and body composition of juvenile red-spotted grouper (7.85 ± 0.03 g fish⁻¹). Nine semi-purified diets were formulated containing varying protein levels (440–520 g kg⁻¹, dry matter) and lipid levels (60–120 g kg⁻¹, dry matter). The weight gain of juvenile Epinephelus akaara was affected by dietary protein (p =.005) and its interaction with dietary lipid (p =.020). Viscerosomatic index, intraperitoneal fat ratio and whole-body lipid level increased with increasing dietary lipid level (p <.001). Nitrogen retention was not affected by dietary protein and lipid, while lipid retention decreased with increasing dietary lipid level (p <.001). The plasma blood urea nitrogen increased with increasing dietary protein level (p =.003). This study showed that diet with 520 g kg⁻¹ protein and 60 g kg⁻¹ lipid with 30.58 mg kJ⁻¹ P:E provided a maximal growth for this species. Moreover, an increase in dietary lipid levels (from 60 to 90 g kg⁻¹) could reduce the protein requirement (from 520 to 480 g kg⁻¹) without affecting the growth performance, while higher fat deposition was observed in fish fed high-lipid diets.