Hazelnut meal as a substitute for soybean meal in extruded feeds of rainbow trout was investigated. The performance of extruded feeds containing hazelnut meal as a substitute for 20% of soybean meal (Diet 2) and 30% of soybean meal (Diet 3) was compared to a nutritionally balanced control (Diet 1) (a commercial trout feed formulation). Each diet was fed to 3 replicate groups (initial BW: :36 +/- 1.37 g; mean +/- SD); the fish were fed the equivalent of 2% of their body weight, 2 times daily (0800 and 1600) for 64 days at 15 +/- 0.11 degrees C under a natural photoperiod. There was no significant difference in weight gain between the control (Diet 1) and Diet 2. Diet 1 produced significantly higher weight gain than Diet 3. The carcass fat content of fish fed a fishmeal and soybean meal diet was significantly higher than that of fish fed the other diets. Weight gain, feed efficiency ratio. relative growth rate, and apparent net protein retention data showed that hazelnut meal had the potential to substitute 20% and 30% of soybean meal in extruded trout feeds.