Enhanced resistance of rainbow trout, Oncorhynchus mykiss, against Aeromonas hydrophila and Yersinia ruckeri challenged with isolated Lactobacilli from common carp intestine

The aim of this study was to examine the use of isolated Lactobacilli from common carpintestine to increase the resistance of rainbow trout against Aeromonas hydrophila andYersinia ruckeri. For this purpose, intestinal content of 115 common carp were collected from the water resources of West Azarbaijan province and cultured on De Man, Rogosa and Sharpe Agar (MRS) medium. Finally four isolated Lactobacilli were used for antagonistic assay after identification based on conventional bacteriologic tests. The in-vitro antagonistic assay by agar diffusion test showed that Lactobacillus casei and L. plantarum inhibited the growth of Aeromonas hydrophila and Yersinia ruckeri. For in-vivo study 720 rainbow trout (20±30 gr) were obtained from a local farm and acclimated to the laboratory conditions for one week and then divided into four groups in three replicates. The bacteria were administered at 5×107 CFU/gr of feed while the control groups received antibiotic and sterile normal saline. The trial was conducted for one month and all treatments were challenged (IP) with two important pathogenic bacteria (Aeromonas hydrophila and Yersinia ruckerii). The results showed that Lactobacillus casei significantly (p<0.05) decreased the rainbow trout mortality against both pathogens than that of untreated control group. During the Lactobacilli feeding periodLactobacillus casei and Lactobacillus plantarum persisted in the fish intestine in highnumbers. Within two weeks after the change to the non-supplemented feed, both Lactobacilli decreased from intestine. In conclusion, the use of non specific and native Lactobacilli could improve rainbow trout resistance against pathogens.