Effects of Lactobacillus on growth parameters, survival rate and resistance of rainbow trout (Onchorhynchus mykiss) to Streptococcus iniae

Abstract

In this study, the effects of Lactobacillus which was isolated from the gut of rainbow trout were evaluated on growth parameters, survival rate and resistance of rainbow trout to Streptococcus iniae. This bacterium was added to the fish diet in 3 treatments (log 7, 8 and 9) and a control treatment was considered. The effects of various treatments on growth parameters and survival were evaluated in day 30 and day 60. At the final stage, resistance of treated fish to streptococcosis was evaluated. The results showed that Lactobacillus was able to improve the growth parameters (weight, feed conversion ratio, protein efficiency ratio, coefficient of obesity, specific growth rate and protein yield coefficient) and survival rate of fish in which the log 8 LAB showed a significant difference compared to the other treatments and the control treatment. The challenge of rainbow trout with Streptococcus iniae indicated that the highest survival rate was observed in the treatment with the log 8 LAB (96.66%), whereas the lowest survival rate was observed in the control treatment (25.38%). These results indicated that Lactobacillus which was isolated from the gut of rainbow trout showed probiotic properties and improved growth parameters of fish. Moreover, it increased the resistance of rainbow trout to streptococcosis.