Effects of dietary LNA/LA ratios on growth performance, fatty acid composition and expression levels of elovl5, Δ4 fad and Δ6/Δ5 fad in the marine teleost Siganus canaliculatus

Abstract

Rabbitfish Siganus canaliculatus is a crucial cultured herbivorous marine teleost, and the first marine teleost demonstrated to have the ability of biosynthesizing long-chain polyunsaturated fatty acids (LC-PUFA) from linolenic (LNA) and linoleic acid (LA) precursors, suggesting the application potential of vegetable oils (VO), rich in LNA or LA but lack of LC-PUFA, as the dietary lipid resources. In the present study, seven diets (D1–D7) were prepared for the culture of rabbitfish juveniles lasting 12weeks. D1 (control diet) contained fish oil (FO) as the sole lipid, while D2–D7 contained a blend of glycerol trioleate and perilla oil with an ALA/LA ratios ranging from 0.05 to 2.45. The results showed that fish fed D3 or D5–D7 displayed as good growth performance as that fed D1. The fatty acid (FA) composition of liver and fillet reflected dietary FA profiles, and relatively higher levels of n-3 LC-PUFA was observed in D5–D7 groups. While the hepatic mRNA levels of ∆4 and ∆6/∆5 fatty acyl desaturase (Fad) and elongation of very long-chain fatty acids (Elovl) genes were affected by dietary LNA/LA ratios, with the highest expression of all three genes in fish fed D6 with an LNA/LA ratio of 1.93. Take the above results together, it can be concluded that diet contained a blend of VO with around 1.93 LNA/LA ratio is suitable for rabbitfish culture concerning the growth performance and LC-PUFA biosynthesis.