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The effect of different levels of fucoidan on fatty acid profile and growth of rainbow trout were investigated. 150 fish (average weight 18.84 ± 70.7) were distributed in 15 fiberglass tanks (100 liters) and fed for 8 weeks at different levels (0 (control), 0.1%, 0.5%, 1% and 2% fucoidan). The results showed that the treatment with the highest amount of fucoidan had the highest final weight, specific growth rate and body weight gain, and there was a significant difference between treatments (p <0.05). There was no significant difference between feed conversion ratio and different treatments (p> 0.05). The difference between EPA, DHA, SFA, MUFA, n-3, HUFA and ratio of n-3 to n-6 was not significant (p >0.05), while PUFA and Arachidonic acid significantly different between treatments (p <0.05) and the highest value was observed in in treatment 2 and 1% respectively. Based on the results of this study, it can be concluded that this type of Polysaccharide at high doses (1 and 2% of fucoidan) can improve the growth performance and maintain the quality of muscle fatty acids.