Efects of dietary probiotic (Lactobacillus rhamnosus) on growth performance, digestive enzymes activity and resistance against infection (Aeromonas hyrophila) in Nile tilapia (Oreochromis niloticus)

Considering that Aeromonas hydrophila bacteria is one of the major pathogens in fresh water aquaculture, in the present study, four fish groups of Nile tilapia (Oreochromis niloticus) with an initial weight of 16 g, were fed for 60 days by diets containing different levels of probiotic Lactobacillus rhamnosus and finally, after measuring the growth performance and digestive enzymes activity, they were injected with Aeromonas hydrophila bacteria and blood indices were measured after complete incidence of the disease. The results showed that, in treatment of 3 g/kg probiotic in diet the final weight and feed conversion ratio were the highest and lowest, respectively. In addition, the trypsin activity in treatment 3 and amylase activity in treatments 2 and 3 was significantly higher than other treatments (P < 0.05). One week after infection by bacteria, the alkaline phosphatase and alanine aminotransferase enzymes in the blood serum decreased in treatments of 2 and 3 g/kg probiotic in diet compared with other treatments, and survival in these groups was higher than other treatments (P < 0.05). Finally, it seems that using 2 to 3 g/kg Lactobacillus rhamnosus in Nile tilapia diet can significantly increase the growth performance as well as the resistance to Aeromonas hydrophila infection.