In this study, rainbow trout were fed for a total of 144 days with different feed mixes containing 0.00%, 0.10%, 0.40%, 0.70%, 1.00% and 1.30% black cumin oil. The effect of black cumin oil on growth performance, feed content and fatty acid composition of rainbow trout was researched. The starting weight of fish in the experimental group was approximately 60 g, which increased to 215.21 +/- 4.12g, 217.32 +/- 3.14g, 235.12 +/- 2.9g, 240.21 +/- 6.5g, 260.14 +/- 4.7g, and 258.89 +/- 1.6g, respectively and the differences in growth between the groups were observed to be statistically significant (p<0.05). Black cumin oil decreased the feed conversion rate of the fish. The addition of black cumin oil in the fish feed increased feed consumption and the daily feed consumed per fish for each group was as follows: 0.93g, 0.93g, 0.97g, 1.00g, 1.02g and 1.02g, respectively. At the end of the experiment the economic conversion rates of the fish ($ Kg(-1)) were between 1.58 and 1.67, while the economic benefit index was between 0.60 and 0.72. The study showed that protein efficiency rates and specific growth rates of the experimental groups had increased. The addition of black cumin oil to the feed increased the proportions of raw protein, oil and raw cinder in the trout and decreased the proportion of moisture, while also increasing the amounts of linoleic, oleic and stearic acids.In conclusion, the addition of 1.00% black cumin oil in feeds increases growth performance in fish and decreases production costs.