Dietary flaxseed (Linum usitatissimum) oil supplementation affects growth, oxidative stress, immune response, and diseases resistance in rainbow trout (Oncorhynchus mykiss)

This paper describes the effects of flaxseed (Linum usitatissimum) oil (FSO) as a feed additive on growth per-formance, oxidative stress, immunity, and disease resistance in rainbow trout (Oncorhynchus mykiss). Eight -hundred-and-forty rainbow trout individuals (mean weight: 25.66 +/- 1.33 g) were fed with different doses of FSO (0.5, 1, and 1.5%) ad libitum two times a day for 9 weeks. At the end of the feeding, growth performance was evaluated and the fish were challenged with two different bacteria (Yersinia ruckeri and Aeromonas hydrophila). At the end of the 3rd, 6th, and 9th weeks, blood and tissue samples were taken from 9 fish per treatment to evaluate innate immune response, cytokine gene expression levels, antioxidant enzyme activities and lipid peroxidation levels, and digestive enzyme activities. Determination of haematological parameters and histo-logical examination was also carried out to evaluate the general health status of the fish. Results showed that the final weight and specific growth rate of FSO-supplemented fish increased significantly (p < 0.05). FSO-supplemented fish showed higher resistance to Y. ruckeri than the control group (p < 0.05). However, sur-vival rates of all groups in A. hydrophila challenge test were similar (p > 0.05). Among the investigated innate immune response parameters, the potential killing activity of phagocytes, myeloperoxidase activity, and lyso-zyme activity increased in the FSO-supplemented groups (p < 0.05). Almost all cytokine gene expression levels in the experimental groups up-regulated especially after 9 weeks of feeding in the head kidney and intestine (p < 0.05). Similarly, superoxide dismutase and catalase activities were found to be significantly higher in the FSO group than in the control (p < 0.05) whereas, the lipid peroxidation levels drastically declined as a result of the FSO supplementation (p < 0.05). These results suggest that FSO can improve growth, enhance immune response, and lower oxidative damage in rainbow trout when supplemented at the rates of 0.5-1.5% for 9 weeks.

Automated summary

This study investigated the effects of flaxseed oil as a feed additive on the growth, oxidative stress, immunity, and disease resistance of rainbow trout. The results showed that the addition of flaxseed oil increased the final weight and specific growth rate of the fish, as well as their resistance to a specific bacteria. Furthermore, flaxseed oil improved the immune response and reduced oxidative damage in the fish.