Improving lipid utilization and growth through lecithin inclusion in diets for giant grouper (Epinephelus lanceolatus)

Giant grouper (Epinephelus lanceolatus) is a culturally and economically significant farmed fish species in Asia and an emerging aquaculture species in Australia. However, the historical reliance on ‘trash fish’ as feed has hindered the development of species-specific formulated diets. Preliminary findings suggest that methionine and choline influence lipid metabolism, highlighting the need to re-evaluate dietary lipid levels for optimal growth. Building on these findings, this study examined how dietary lipid levels and phospholipid (lecithin) inclusion interact to influence lipid metabolism and growth performance in E. lanceolatus. Six isoproteic diets (44.47 ± 0.05 % protein) were formulated with 10 % or 15 % lipid and 0, 0.5 %, or 1 % lecithin inclusion. The results showed that increasing lipid content from 10 % to 15 %, combined with 1 % lecithin inclusion, enhanced weight gain by 12.14 %. This growth-promoting effect was associated with elevated circulating triglycerides and altered cholesterol and glucose levels, suggesting improved lipid transport and utilization. In contract, no growth improvement was observed with 0 % or 0.5 % lecithin inclusion. These findings demonstrate the critical role of lecithin in optimizing lipid metabolism and growth performance in juvenile E. lanceolatus, providing a foundation for sustainable, species-specific diet formulations.