In this study Bacillus subtilis is used for control of streptococcosis with the agent of Streptococcus iniae in Rainbow trout. The experience was carried out in 2 groups (Control and Treatment) and 3 replicates. In Control group, probiotic was not applied in diet but in Treatment group, Bacillus subtilis was administered in feed at a concentration of 10 7 cells g-1. In the day of forty five, 0.1 ml intraperitoneally injection of S.iniae with 2×10 7 cells ml-1 dosage was done for both of groups and were checked for the rest of the survey duration (2 weeks). At the end of the time which took about two months, blood samples were caught for biochemical experiments for realizing the effect of B.subtilis feeding on resistance of fish against S.iniae infection. After injection of S.iniae, there was no significant difference among Control(C) and Treatment(T) groups considering parameters such as glucose and aspartate aminotransferase (p>0.05). But significant difference was seen in the serum total protein, serum albumin, IgM, lysozyme, 38 M. Kamgar, R. Pourgholam, M. Ghiasi and M. Ghane urea, Alanin aminotransferase and alkaline phosphatase in both groups (p<0.05). The serum total protein, serum albumin, IgM and lysozyme were higher in T group and urea, Alanin aminotransferase and alkaline phosphatase were lower in comparison with the control. The results of the present study indicate that B.subtilis can be used as an agent for the control of streptococcosis in Rainbow trout hatchery and culture farms for decreasing economical disasters.

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