Changes in Immunity, Expression of some Immune-Related Genes of Shabot Fish, Tor grypus, Following Experimental Infection with Aeromonas hydrophila: Effects of Autochthonous Probiotics.

In this study, the effects of orally administrated two native probiotics (Lactobacillus plantarum and Lactobacillus delbrueckii ssp. bulguricus), isolated from the intestine of Shabot fish, Tor grypus, on some immune response parameters and immune-related genes expression against Aeromonas hydrophila in T. grypus were evaluated. Four hundred and eighty juveniles weighing 45 ± 10 g were randomly divided into four groups (with three replications) and fed with the experimental diet containing 5 × 107  cfu g-1 of L. plantarum (G1), Lactobacillus bulgaricus (G2), Lactobacillus casei (G3), and a control diet (without probiotics) for 60 continuous days. At the end of the dietary treatments, fish were challenged with a lethal concentration of A. hydrophila (5 × 108  CFU ml-1 ) via intra peritoneal (i.p) injection. Blood and head kidney samples were taken from six fish in each treatment before challenging and 6, 12, 24, and 48 h and also 7 days after injection. The results showed that lysozyme, complement, bactericidal, and NBT activity of probiotic-treated groups were significantly elevated (P < 0.05). The IL-8, IL-1β, and TNF-α gene expressions were significantly higher in all probiotic-treated groups (P < 0.05). Meanwhile, a high direct correlation was observed between serum immune parameters and expression of immune-related genes (P < 0.0001); furthermore, the highest correlation (R 2  = 0.634, P < 0.0001) was recorded between IL-1β expression and NBT activity. It can be concluded that not only two native probiotics strains stimulate serum immune responses parameters and immune-related gene expression in T. grypus, but also a high correlation was seen among these indices. The study suggests that gastrointestinal colonization is preferred for host specificity as the strain previously derived from shabot fish displayed better colonization than the non-indigenous bacteria strain such as L. casei. Therefore, these native probiotics bacteria can be accounted as suitable candidates to immune stimulation in fish.