Seawater Culture Increases Omega-3 Long-Chain Polyunsaturated Fatty Acids (N-3 LC-PUFA) Levels in Japanese Sea Bass (Lateolabrax japonicus), Probably by Upregulating Elovl5

SIMPLE SUMMARY: Japanese sea bass can be farmed in both marine and inland waters, and marine cage cultured fish have a higher polyunsaturated fatty acid content and tastes better. However, how marine cage rearing improves its polyunsaturated fatty acid content has not been clarified yet. Thus, we investigated the role of fatty acid desaturase 2 and fatty acid elongase 5, two key players in fatty acid metabolism, in long-chain polyunsaturated fatty acids biosynthesis in Japanese sea bass under seawater culture. We found that the content of eicosapentaenoic acids (EPA) and docosahexaenoic acids (DHA) in the seawater group was significantly higher than in the freshwater group, and the fatty acid elongase 5 gene expression level in the seawater group was significantly higher than in the freshwater group. On the other hand, however, the fatty acid desaturase 2 expression level in the seawater group was significantly lower than in the freshwater group. A further comparison of gene promoter methylation patterns of fatty acid desaturase 2 and fatty acid elongase 5 showed that seawater reared fish were less methylated in the fatty acid elongase 5 promoter region, but far more methylated in fatty acid desaturase 2 promoter region. Taken together, our study suggests important roles of fatty acid elongase 5 in the enhanced biosynthesis of long-chain polyunsaturated fatty acids under marine cage culture compared with freshwater pond culture. ABSTRACT: The fatty acid compositions of the fish muscle and liver are substantially affected by rearing environment. However, the mechanisms underlying this effect have not been thoroughly described. In this study, we investigated the effects of different culture patterns, i.e., marine cage culture and freshwater pond culture, on long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in an aquaculturally important fish, the Japanese sea bass (Lateolabrax japonicus). Fish were obtained from two commercial farms in the Guangdong province, one of which raises Japanese sea bass in freshwater, while the other cultures sea bass in marine cages. Fish were fed the same commercial diet. We found that omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) levels in the livers and muscles of the marine cage cultured fish were significantly higher than those in the livers and muscles of the freshwater pond cultured fish. Quantitative real-time PCRs indicated that fatty acid desaturase 2 (FADS2) transcript abundance was significantly lower in the livers of the marine cage reared fish as compared to the freshwater pond reared fish, but that fatty acid elongase 5 (Elovl5) transcript abundance was significantly higher. Consistent with this, two of the 28 CpG loci in the FADS2 promoter region were heavily methylated in the marine cage cultured fish, but were only slightly methylated in freshwater pond cultured fish (n = 5 per group). Although the Elovl5 promoter was less methylated in the marine cage reared fish as compared to the freshwater pond reared fish, this difference was not significant. Thus, our results might indicate that Elovl5, not FADS2, plays an important role in the enhancing LC-PUFA synthesis in marine cage cultures.