In this study, the effect of two Gram-positive bacteria, Lactococcus lactis and Bacillus sp., on the survival rate of rainbow trout (Oncorhynchus mykiss) eggs until larval stage. And also, effects of bacteria on some water quality criteria and blue sac fry syndrome on alevin stage of fish was investigated during this period. The bacteria contaminated on healthy trout eyed eggs during the incubation period by the immersion method. Two bacterial groups and the control group were designed in duplicate. At the end of the study (fry stage), the survival rates of the eggs were recorded. It was also investigated whether the bacteria reduced the ammonia, nitrite, nitrate and phosphate content of the water and prevented the blue sac syndrome caused by Aeromonas hydrophila. The highest survival rate was observed in trout inoculated with Bacillus sp. (92.5%), followed by L. lactis (70%), and control (45%), respectively. The highest death rates were observed during the alevin stage in all groups. In this study, it was observed that both species of bacteria contributed to the survival rate of the trout eggs during the incubation period. It was determined that both species of bacteria reduced the amount of nitrite in the water. Furthermore, with this study, Bacillus sp. was observed to suppress the effects of blue sac fry syndrome caused by A. hydrophila.
