Abstract:Lipid is the second largest nutrient source of fish, plays an important role in the nutrient metabolism. As the essential fatty acid, the main component of lipid, long chain highly unsaturated fatty acids (LC-HUFA) plays an important role on regulating metabolism and maintaining cell morphology. The synthesis of LC-HUFA involves many biological processes such as fatty acid transport, de novo synthesis, β-oxidation, desaturation, and carbon chain elongation. A stable LC-HUFA metabolic pattern has been formed through long-term evolution. Previous studies have shown that exogenous intake can increase LC-HUFA accumulation and regulate metabolism in juvenile fish, however, there are few studies on larvae. Early nutritional programming can affect the metabolic of the body, accompanied by epigenetic regulation at times. There are a great significance to explore how to activate LC-HUFA synthesis limitation by early nutrition programming in fish, and further regulated by epigenetic mechanisms. The study explored the effects of docosahexaenoic acid (DHA) nutrition programming on the viability, fatty acid deposition and epigenetic modification of fatty acid metabolism in larvae of Cynoglossus semilaevis to provide a theoretical basis for the development of high-quality fish of Cynoglossus semilaevis. Hatchling of Artemia salina was fortified with DHA fortifier. Larvae of Cynoglossus semilaevis feed with fortified Artemia salina was used as the experimental group, and feed with unfortified Artemia salina was used as the control group. The larvae was cultured for 15 days post hatching (15dph), and the hatching rate, survival rate, malformation rate and body length was recorded. The whole body fatty acid profile and gene expression of fatty acid metabolism of larvae was detected. The DNA methylation status of fads2 gene was analyzed. Survival rate and body length of the experimental group was significantly increased, and the malformation rate was significantly decreased (P<0.05) at 15dph. The contents of linoleic acid (LA), arachidonic acid (ARA), linolenic acid (LNA), DHA, n-6PUFA and n-3PUFA increased significantly (P<0.05). The expression levels of pparα, acc1 and fas genes was significantly decreased, fads2 and fabp1 was significantly increased, and there was no significant difference in the expression level of elovlα (P>0.05). There was a CpG island from -750bp to -1050bp from the fads2 transcription start site, and the total length of the fragment was 301bp. There was 8 candidate CpG sites, of which 5 CpG sites was significantly demethylated (P<0.05). The fads2 promoter region was highly demethylation in terms of overall methylation levels(P<0.05). In this study, nutrition programming of larvae of Cynoglossus semilaevis with DHA can improve the survival ability of larvae, enhancing LC-HUFA synthesis by promoting fatty acid transport and desaturation in larvae to improving fatty acid metabolism. Early nutritional programming is involved in the demethylation of fads2 promoter which promoted the transcription of fads2 gene, this is one of the root causes of the increase in LC-HUFA. This study is helpful to develop high LC-HUFA quality larvae of Cynoglossus semilaevis, and provide a new idea for efficient breeding of Cynoglossus semilaevis.
