The use of lactic acid bacteria from human origins as a potential probiotic supplementation in aquaculture
feed is now widely accepted. Here, we examined some of the properties and mechanisms of the
action of Lactobacillus rhamnosus GG, originating from humans, on growth performance, gut mucosal
immunity and humoral and cellular immune response in tilapia (Oreochromis niloticus). The results suggested
that supplementation of L. rhamnosus gave an advantage in promoting the intestinal structure and
the mucosal immunity of tilapia. Probiotic fish had a greater villous height in all parts of the intestines
and, significantly, in the proximal and middle part. The population of intraepithelial lymphocytes was
significantly higher in the probiotic group than in the control group in all parts of the intestines. The population
of acidophilic granulocyte in the probiotic group was significantly higher at the proximal and distal
parts when compared with the control group. The higher serum complement activity as well as the
enhanced phagocytosis and killing ability of the head kidney leukocytes in the probiotic supplemented
fish corresponded with the higher level of TNF alpha and IL-1 gene expression, suggesting that the induction
of IL-1 and TNF alpha cytokines by L. rhamnosus served as an important regulator of gut associated
immune systems.