Characterization, mRNA expression and regulation of Δ6 fatty acyl desaturase (FADS2) by dietary n − 3 long chain polyunsaturated fatty acid (LC-PUFA) levels in grouper larvae (Epinephelus coioides)

•The FADS2 of grouper showed activities of Δ6 desaturase and Δ8 desaturase.•FADS2 is the rate-limiting enzyme in grouper LC-PUFA biosynthetic pathway.•Dietary n − 3 LC-PUFA could regulate the FADS2 mRNA expression of grouper larvae.

N − 3 long chain polyunsaturated fatty acids (LC-PUFAs) are essential for marine fish to maintain normal growth and physiological functions, although the ability of LC-PUFA biosynthesis is limited. FADS2 was chosen to investigate its characterization, mRNA expression and regulation by dietary n − 3 LC-PUFA in the present study due to its being considered as the rate-limiting enzyme involved in LC-PUFA biosynthetic pathway. The FADS2 of grouper, when expressed in yeast, was shown to desaturate 18:3n − 3 and 18:2n − 6, indicating that it coded for a Δ6 desaturase enzyme. Lower desaturation of 20:3n − 3 and 20:2n − 6 indicated trace Δ8 activity. Following 4 weeks of feeding trial, the FADS2 mRNA expressions of grouper larvae that were fed diets with different LC-PUFA levels were measured and results showed that the expression of FADS2 increased significantly with dietary LC-PUFA from 0.52% to 0.94% and then decreased significantly (P < 0.05). The different growth performance and fatty acid composition of grouper among five treatment larvae also demonstrated that though the ability to synthesize LC-PUFA in grouper larvae was limited. These results showed that the FADS2 of grouper also displayed Δ8 desaturase ability when expressed in yeast, and dietary n − 3 LC-PUFA could regulate the biosynthesis of LC-PUFA through influencing the expression of FADS2.