In this paper the effect of replacing fish meal with different protein sources was tested on growth performance, feed utilization and digestive enzyme activity in rainbow trout. Six experimental diets containing different protein sources were tested: 1) 100% fish meal (FM), 2) 60% fish meal + 40% plant protein (60FM/40PP), 3) 30% fish meal + 70% plant protein (30FM/70PP), 4) 100% plant protein (PP), 5) 50% poultry byproduct meal protein + 50% plant protein (50PP/50PM) and 6) 100% poultry by-product meal (PM). Rainbow trout with a mean initial weight of 15±2 g were fed experimental diets for 60 days. Results showed that 40% fish meal replacement with plant protein did not negatively affect the growth indices, feed utilization and muscle proximate composition. However, 70% and 100% replacement of fish meal with different protein sources resulted in significantly decreased growth, feed utilization and total fillet protein, but significantly increased total fillet lipid. The alkaline protease activity in 60FM/40PP, 50PM/50PP and PM groups were not significantly different with control, but significantly lower in 30FM/70PP and PP groups. The fish fed 100% plant protein (PP) resulted in decreased lipase activity compared to other feeding treatments, but no significant differences in lipase activity among other groups