The aim of this study was to investigate the effect of fermented silage on growth performance and apparent digestibility of protein at feed of rainbow trout. In this study, Anchoy Kilka meal were mixed with 25% wheat flour and inoculated with microorganisms (10⁸ cell/ml) and kept in an incubator for 14 days at 37 ºC. Fermentation of Anchoy Kilka has resulted in a significant increase in moisture, protein and pH values at the end of the period. Ash content of the fermented product was almost twice as that of the unfermented fish meal in all of the samples. Fiber and crude fat contents of the fermented product was respectively reduced and increased (p<0.05) in comparison with the initial product. Replacement of fish meal with fermented silage (0, 25, 50, 75 and 100%) showed that there was significant difference in growth performance and apparent digestibility protein (p<0.05). Fish fed with 25 percent fermented silage had the best of growth performance and apparent digestibility of protein (p<0.05). In conclusion, the results of this study suggest that fish meal produced with fermentation manner can be used as good alternative for feedstuff of rainbow trout.