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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.
Wang et al. (Tue,) studied this question.