Mechanisms of lipid metabolism and transport underlying superior performance of Senegalese sole (Solea senegalensis, Kaup 1858) larvae fed diets containing n-3 polyunsaturated fatty acids

Abstract

To date, most research on larval lipid nutrition has been centered on essential fatty acid requirements. However, less is known about effects of dietary fatty acid (FA) composition on lipid absorption and metabolism, as addressed in this study. Senegalese sole were fed live preys enriched with different oils: cod liver oil (CLO), linseed oil (LSO), soybean oil (SBO), and olive oil (OO), that are rich in long-chain polyunsaturated FAs (LC-PUFA), n-3 PUFA, n-6 PUFA or monounsaturated FAs (MUFA), respectively. Larvae reared on CLO showed significantly improved growth and survival, faster onset of metamorphosis and maturation of the intestine, lower lipid accumulation in liver after metamorphosis and an up-regulation of genes involved in lipid transport and phospholipid metabolism, while key lipogenesis genes were down-regulated. From the remaining treatments, the LSO diet induced the closest performance to CLO, with larvae completing metamorphosis at a similar time and having the second best growth and survival by the end of the experiment. They were also grouped closer to the CLO treatment than the remaining vegetable oil treatments, based on the patterns of gene expression. These results showed that oil sources rich in LC-PUFA and n-3 PUFA were superior to those having high n-6 PUFA or MUFA levels in the larval nutrition of Senegalese sole and indicate that this effect might be at least partly explained by an up-regulation of phospholipid metabolism and apolipoprotein synthesis, likely leading to enhanced lipid transport and mobilization, as well as tissue growth and remodeling. Statement of relevanceThe nutritional and physiological roles of dietary C18 PUFA in the absence of LC-PUFA have rarely been investigated in fish, particularly in larvae, as it is unfeasible to culture most marine species in such extreme dietary conditions. Senegalese sole (Solea senegalensis), a marine species of high commercial aquaculture importance in southern Europe, has relatively low LC-PUFA requirements during the larval stage compared to other marine finfish, making it a good model species to investigate this subject. A holistic approach was implemented to determine the effects these FAs may have on fish performance and metabolism, by analyzing growth, development, intestinal maturation, lipid and FA composition, hepatic and intestinal lipid accumulation, and expression of genes involved in lipid metabolism, absorption and transport (qPCR).