In this trial, the lipid contents and fatty acid compositions (% of total fatty acids) of rainbow trout fed with four different ratios of clinoptilolite were studied. The fatty acid compositions of fish in groups ranged from 26.81% to 27.93 % saturated fatty acids, 25.35–31.435 % monounsaturated and 32.99–40.185 % polyunsaturated. Among them, those occurring in the highest proportions were oleic acid (C18:1n9, 19.85-22.27 %), palmitic acid (C16:0, 15.60-16.56 %), linoleic acid (C18:2n6, 11.43-18.88 %), cis-4,7,10,13,16,19-docosahexaenoic acid (C22:6n3, 13.36-15.52 %), stearic acid (C18:0, 4.25-4.75 %), palmitoleic acid (C16:1, 3.53-4.59 %), cis-5,8,11,14,17-eicosapentaenoic acid (C20:5 n3, 3.11-3.39 %), and myristic acid (C14:0, 2.56-2.85 %). The findings demonstrated that fatty acid compositions of the groups depend on feed, age, environmental conditions, and effects of feed additives like clinoptilolite. In this respect, it demonstrated that clinoptilolite can be added to fish feeds