Vitamin B6 supplementation increases the DHA concentration of muscle lipids of rainbow trout (Oncorhynchus mykiss)

Fish fillet quality is influenced by feed quality. In particular, vitamin B6 availability improves growth rate and nutritional value, because it is related to protein and lipid metabolism. The present study investigates the effect of increasing amounts of vitamin B6 on growth, fatty acid composition and lipid peroxidation of muscle tissue of rainbow trout (Oncorhynchus mykiss). Quadruplicate groups of trout of a mean initial weight of 110 g were fed commercial diets supplemented with four different quantities of vitamin B6 (0, 10, 25 and 50 mg kg−1 diet). Over the experimental period, there were no significant differences in weight gain and feed intake, while vitamin B6 concentration of muscle was affected by dietary intake, even though its increase was not proportional to the concentrations in the feed. The fatty acid composition of muscle lipid showed differences between the four groups. The percentage of long‐chain unsaturated fatty acids, in particular docosahexaenoic acid, increased significantly in vitamin B6‐supplemented groups. However, despite the increased fatty acid unsaturation index, lipid peroxidation parameters such as vitamin E content, malondialdehyde production, glutathione reductase and glutathione peroxidase activities did not show significant differences, meaning that the higher level of long‐chain unsaturated fatty acid did not increase the muscle susceptibility to oxidative stress.