In this study, sea buckthorn oil (SBO) was added to rainbow trout fish diets at 0.25%, 0.5%, and 1% rates in order to determine the effects on growth, feed conversion rate, survival rate, fillet quality, and physiological, biochemical and histopathological parameters. The experiment was designed in four groups with three replicates each including 20 fish with 18 ± 3 g and lasted for 45 days. Fish were fed three times a day and weighed biweekly. At the end of the experiment, significant differences were determined with respect to specific growth rates (SGR), weight gains (WG), and feed conversion ratios (FCR) (P <
0.05), except for survival ratios (SR) (P >
0.05). Sea buckthorn oil improved fish fillet quality and weight gain rates by up to 27% compared to control. The pepsin, amylase, lipase, and trypsin enzyme activities differed significantly (P <
0.05) from those of the control group. Serum lysozyme myeloperoxidase (MPO) and plasma nitro blue tetrazolium (NBT) levels differed significantly (P <
0.05) in the 0.5% and 1% groups compared to the control group, except for the 0.25% group. Liver catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and malondialdehyde (MDA) levels significantly differed in all groups, especially in the 0.5% and 1% groups compared to the control group (P <
0.05). SBO supplementation to feed caused significant changes in the FA profiles, especially 18:00 in ∑SFA
16:1 in ∑MUFA
20:5n-3 and 20:2n-6 in ΣPUFA
20:5n-3 in ∑n-3
and 20:2n-6 in ∑n-6 in rainbow trout (P <
0.05). There were no histopathological changes between the control and the experimental groups. The determined data suggested that 1% SBO may be successfully used as a feed additive in rainbow trout.