Optimal Dietary Lipid Requirement for Juvenile Leopard Coral Grouper (Plectropomus leopardus)

Leopard coral grouper (Plectropomus leopardus) is a high-value marine species increasingly produced under intensive farming conditions; however, its dietary lipid requirement remains poorly defined, hindering the development of cost-effective formulated feeds. This study aimed to determine the optimal dietary lipid level for juvenile P. leopardus by assessing growth performance, hepatic lipid metabolism, and antioxidant capacity in response to graded lipid inclusion. Juveniles (initial body weight [IBW]: 13.94 ± 0.07 g) were fed six isonitrogenous diets (53% crude protein) containing 6%, 8%, 10%, 12%, 14%, or 16% lipid for 9 weeks (three replicate tanks per diet; 27 fish per tank). Weight gain (WG) and specific growth rate (SGR) increased with dietary lipid up to 10% and then declined. Intestinal lipase activity increased with dietary lipid level. Dietary lipid at 8%-12% improved hepatic lipid metabolic balance, as indicated by reduced activities of lipogenic enzymes (malate dehydrogenase [MDH], glucose-6-phosphate dehydrogenase [G6PD], and fatty acid synthase [FAS]) and increased lipoprotein lipase (LPL) activity (p < 0.05). Dietary lipid at 8%-12% also enhanced antioxidant defenses, reflected by higher glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities in serum, liver, and hindgut, without an increase in malondialdehyde (MDA). In contrast, high-lipid diets (14%-16%) induced hepatic lipid metabolic imbalance followed by pronounced hepatic lipid deposition (histological staining and increased hepatic crude lipid; p < 0.05), elevated serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, and significantly increased MDA levels in serum, liver, and hindgut (p < 0.05), while antioxidant enzyme activities tended to decrease, indicating heightened oxidative stress. Overall, growth performance was highest at ~10% dietary lipid under the present experimental conditions, and quadratic regression analysis suggested an approximate optimum near 9.3%. Moderate dietary lipid (8%-12%) promoted growth by improving hepatic lipid metabolism and antioxidant capacity, whereas excessive lipid inclusion (≥14%) induced excessive hepatic lipid accumulation and oxidative damage in P. leopardus.