Technical Abstract: Plant protein levels in aquafeeds are increasing in response to the high cost and limited availability of fishmeal for production of animal feeds. The purpose of this study was to evaluate the effects of plant protein blends on growth and feed utilization of rainbow trout (Oncorhynchus mykiss) and to test the top performing blends in diets for Atlantic salmon (Salmo salar) parr. Nine experimental diets containing 33%, 66% and 100% of a soy protein concentrate blend, a corn gluten meal blend or a barley protein concentrate blend and a fishmeal control diet were fed to rainbow trout (initial weight 20g) for 12 weeks. Weight gains of trout fed the soy protein concentrate blend diets and the fishmeal diet were similar, except at the highest level of fishmeal replacement. Weight gains of trout fed the corn gluten meal diets and barley protein concentrate diets were significantly lower than that of fishmeal diet-fed trout at 33%, 66% and 100% level. The soy protein blend and a modified corn gluten blend containing wheat gluten were then evaluated in feeds for Atlantic salmon parr (initial weight 5.46g). Atlantic salmon were fed either a fishmeal control diet or one of six test diets in which 50%, 66% or 84% of fishmeal was replaced with a plant protein blend. Salmon fed diets containing either the soy or wheat gluten protein blends had significantly lower weight gains and higher feed conversion ratios compared to fish fed the fishmeal diet at all levels of fishmeal substitution. Feed intake was reduced in both rainbow trout and Atlantic salmon as plant-based protein increased in the feed. Juvenile rainbow trout appear to tolerate high levels of plant-based protein in their diets, while growth of Atlantic salmon parr was reduced when plant-based proteins were included in their diets.