A 56-day feeding trial was conducted to evaluate the effects of varying dietary lipid and starch levels on growth performance, biochemical components, and hepatic glycolipid metabolism in hybrid grouper. Nine isonitrogenous diets were formulated to contain three levels of lipid (6%, 10%, or 14%) and starch (14%, 21%, or 28%) using a 3 × 3 factorial design. Juvenile fish (initial body weight: 19.06 ± 0.03 g) were randomly allocated to 27 floating net cages (25 fish per cage, three replicates per diet) in an indoor seawater recirculation system and hand-fed to apparent satiation twice daily. Two-way ANOVA was conducted to check treatment effects of dietary lipid and starch levels. No interaction effect between lipid and starch on growth and feed utilization was observed across all treatments; however, significant interactions between the two were observed for condition factor (CF), and some serum biochemical indicators and some hepatic glycolipid metabolic enzyme activities. Growth rate, specific growth rate, and feed efficiency (FE) exhibited a declining trend with increasing dietary lipid levels (p < 0.05). Conversely, hepatosomatic index (HSI), viscerosomatic index (VSI), condition factor, hepatic lipid and glycogen contents, muscle lipid content, serum triglyceride and high-density lipoprotein cholesterol contents, as well as hepatic carnitine palmitoyltransferase 1 (CPT-1) and lipoprotein lipase (LPL) activities, showed an increasing trend (p < 0.05). As lipid levels increased, serum total cholesterol (TC) and total protein (TP) contents dropped to a minimum at the intermediate lipid level (10%) and then rose, regardless of starch level. Hepatic fructose-1,6-bisphosphatase (FBP) activity increased significantly when lipid level rose from 6% to 10% (p < 0.05). With increasing dietary starch levels, HSI, VSI, hepatic and muscle glycogen contents, and serum low-density lipoprotein cholesterol content increased, while FE and serum TP content decreased (p < 0.05). Hepatic CPT-1, LPL, FBP, and pyruvate kinase activities were significantly enhanced when starch levels increased from 14% to 21% or 28% (p < 0.05). Serum aspartate aminotransferase activity was significantly higher in fish fed 14% lipid compared to those fed 6% or 10% lipid. These findings indicate that there is no interaction of dietary lipid and starch on growth and feed utilization, but high dietary lipid (14%) may enhance hepatic lipid oxidation while suppressing glycolysis, thereby limiting growth and promoting hepatic lipid deposition. The results provide a practical reference for optimizing dietary lipid and starch levels in cost-effective feed formulations for hybrid grouper.
Li et al. (Thu,) studied this question.