This study aims to determine the appropriate egg powder ratio that can be substituted into the fish meal to close the protein deficit without adversely affecting the development performance of rainbow trout fry (Oncorhynchus mykiss) (0.38 +/- 0.01 g and 3.55 +/- 0.05 cm). Also, the effects of egg powder used as a protein source on rainbow trout feed on growth performance, feed utilization, body composition, and survival rates were investigated. The egg powder ratio in the ration of the groups were arranged to be 0% (Control), 25% (E-25), 50% (E-50), 75% (E-75), and 100% (E-100) of the amount of protein obtained from fish meal. To evaluate their growth performance, fish were fed for 90 days between March and May, and additional feeding was given for 17 days for the challenge test. As a result of the study, when the more than 25% egg powder was added to the ration, the final body weight (FBW), weight gain (WG), weight gain rate (WGR), specific growth rate (SGR), feed intake (FI), and protein efficiency ratio (PER) had a statistically significant difference among the groups (p<0.05). It was determined that the difference between groups was insignificant in terms of condition factor (CF), and the addition of more than 25% egg powder to the ration increased the feed conversion ratio (FCR) statistically and significantly (p<0.05). As a result of the challenge test carried out with two different fish pathogens (Lactococcus garvieae and Yersinia ruckeri), it was determined that the addition of egg powder decreased the survival rate in all groups compared to the control group (p<0.05). As a result, it was concluded that up to 25% of egg powder can be used rainbow trout fry feeds, but continuous feeding with egg powder supplemented feeds may cause fish health problems.