The effects of high dietary methionine and taurine are not equal in terms of growth and lipid metabolism of juvenile California Yellowtail (Seriola dorsalis)

The aim of this study was to investigate the effects of methionine and taurine supplementation (individually or in combination at individual levels of 10 g/kg) on growth performance and lipid metabolism in juvenile California Yellowtail. A total of 4 dietary treatments were designed as CONTROL, MET, TAU and MET +TAU. After 6 weeks, production performance was significantly increased by dietary taurine and no synergetic effect of dietary taurine-methionine was noticed. Supplementation of methionine as a taurine precursor was not as efficient as providing intact taurine. Fish fed TAU and MET + TAU diets outperformed those fed CONTROL and MET diets in terms of WG, SGR, TCG, CF, and FCR. No significant differences among experimental diets were observed for final weight, HSI, VSI, and bile index. Proximate composition of the whole-body was not influenced by dietary treatments, however muscle protein, lipid, and ash were significantly influenced by dietary treatments. Tissue fatty acid profiles were significantly modified by dietary treatments. The muscle of fish fed taurine-supplemented diets exhibited greater levels of 16:0, SFAS, and 20:5n-3, and reduced levels of 22:5n-3, 22:6n-3, n-3 fatty acids, PUFAs, LC-PUFAs, and DHA/EPA compared to those fed CONTROL and MET diets. Dietary treatments caused a decreasing effect over the change in fatty acids, whole-body (Djh = 3.0-7.9), liver (Djh = 1.5-4.6), and muscle (Djh = 1.5-3.0). The whole-body taurine content significantly increased in taurine-supplemented diets compared to the CONTROL and MET diets. Dietary treatments did not significantly modify cholesterol content in liver, muscle, whole-body, and plasma. No evidence of LC-PUFA synthesis was displayed even though the relative expression of fatty acid synthase (fas) and elongation of very long-chain fatty acids (elovl) were significantly increased in MET-supplemented diets compared to the CONTROL and TAU diets, whereas the fatty acid desaturase (fadsd) was upregulated in MET and CONTROL diets in comparison to the other dietary treatments. The present study highlights the benefits of taurine supplementation to support the growth of juvenile California Yellowtail, however, its effects on reducing tissue lipid content and muscle n-3 fatty acids should be considered.