Influences of low salinity and dietary fatty acids on fatty acid composition and fatty acid desaturase and elongase expression in red sea bream Pagrus major

This study investigated the effects of dietary fatty acids and water salinity on fatty acid composition and expression of the fatty acid desaturase (fads)-like and elongase (elovl)-like genes of red sea bream Pagrus major. Sequence and phylogenetic analyses revealed that the fads-like and elovl-like genes isolated in this study encoded fads6 and elovl5, respectively. There was no significant difference in growth performance or proximate composition of fish fed diets formulated with 100% fish oil (FO) (FO diet) or with 67% of FO substituted with canola oil (VO diet). Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents were significantly higher in liver of fish reared at 15 and 20 ppt than those at 33 ppt. The liver fatty acid desaturase gene transcript was detected by reverse-transcription polymerase chain reaction (RT-PCR) in liver of fish fed the VO diet at 15 ppt, but not at either 20 or 33 ppt. The elovl5 gene was clearly expressed in liver for all treatments. These results suggest that red sea bream could synthesize EPA and DHA from their precursors in liver and that EPA and DHA biosynthesis potency was stimulated at lower salinity.