Effect of different levels of Lactobacillus casei as probiotic on survival and growth performance of rainbow trout (Oncorhynchus mykiss) fingerlings

Probiotics are generally defined as a live microbial food supplement which improve the balance of the host animal’s intestinal flora and the absorption of nutrients from the intestine. The aim of this study was to evaluate the effect of different levels of Lactobacillus casei</em> (PTCC1608) on survival andgrowth performanceof rainbow trout (Oncorhynchus mykiss</em>)fingerlings. Four thousand eight hundred fingerlings (average weight 32.6±5.5g) were randomly divided into 4 groups with three replicates (each with 400 fish). The control group fed with basal diet and the other groups were fed with 5×106</sup> (A), 5×107</sup> (B) and 5×108</sup>(C) CFU/mL L. casei</em> for 60 days. Biometry of specimen was down at 0, 30 and 60 days of study and growth performance rate evaluated. Results showed that fish were fed with 5×106</sup> (A) of L. casei </em>had significant impact (P<0.05) on growth performance. The specific growth rate (SGR), BWG and RGR had best performance at 5×106</sup> (A) of L. casei </em>andshow Significant differences compared with control treatment (P<0.05), while in the diet fed diet with 5×108</sup>(C) CFU/mL of L. casei</em>, some growth and survival indices decreased compared to the control group (P<0.05). There was no change in growth indices in diet fed with diet containing 5×107</sup> (B) CFU/mL of L. casei</em> compared to control in different stages of sampling. Survival rate was significantly different between treatments, so that the highest losses were related to 5×108</sup>(C) CFU/mL of L. casei</em>, which had a significant difference with control group. Results showed that adding 5×106</sup> (A) of L. casei</em> to rainbow trout diet as the most suitable concentration, improved the fish growth indices, but the higher concentrations of this probiotic has negative effects on growth.