Optimal dietary phospholipid requirement for juvenile leopard coral grouper (<i>Plectropomus leopardus</i>)

The highly sought-after carnivorous leopard coral grouper (Plectropomus leopardus) in seawater is valued for its vivid coloration and nutritional richness. Dietary phospholipid supplementation has been demonstrated to enhance physiological health in fish, but these effects are species-dependent. Despite its popularity, there is scarce study regarding the effects of dietary phospholipids on P. leopardus. To determine the optimal dietary phospholipid requirement for P. leopardus, 6 isonitrogenous (53% crude protein) and isolipidic (12% crude lipid) diets were formulated with varying levels (0%, 1%, 2%, 3%, 4%, and 5%) of phospholipid provided by soybean lecithin (SL). Juvenile P. leopardus with an average initial weight (13.92 g) underwent a 9-wk feeding trial. Results demonstrated that weight gain rate (WGR) tended to elevate firstly with the dietary SL content up to 3%, and subsequently diminished. The feed conversion ratio gradually declined with dietary SL level up to 2% and then stabilized. The incorporation of 2% to 5% SL into the diet led to an enhancement of trypsin and lipase activities in the foregut. Additionally, the higher muscular layer thickness, villus width, and villus height in the hindgut were observed with the same dosage of dietary SL. Similarly, the dietary inclusion of 2% to 3% SL boosted the serum and hepatic superoxide dismutase activity, along with enhancing the activities of glutathione peroxidase and lysozyme in liver and hindgut. Furthermore, the dietary incorporation of 2% SL led to an upregulation of the relative mRNA levels of toll-like receptor 2, myeloid differentiation factor 88 (MyD88), and transforming growth factor β1 in the hindgut, but decreased the aspartate aminotransferase and alanine aminotransferase activities in serum. Overall, dietary incorporation of 2% to 3% SL improved the growth rate, digestive function, antioxidant and immune responses of P. leopardus, the recommended level was 3% based on WGR.