The aims of this study were to evaluate the inclusion of different concentrations of Lactobacillus plantarum in Nile tilapia diet and to verify histological effects on tissues of the animal organs, as well as to verify its effects on growth parameters and possible increase in the immune system. A total of 240 juveniles were distributed in 16 tanks arranged in a recirculation system. One control group and three treated groups (104, 106, and 108 colony-forming unit (CFU) g -1L. plantarum kg feed-1) were established in quadruplicate. After 35 days of supplementation, it was not possible to observe differences in growth rates and hematological parameters. However, in the kidney, there was a reduction in the presence of PAS-positive granular leukocytes (PAS-GL) between the collections (15 and 35 days). The liver had lower number of lesions related to loss of cordonal aspects of fish fed 108 CFU g-1 on day 15. Fish fed 104 and 108 CFU g-1 showed lower degree of congestion at day 35. The probiotic also provided a reduction in the number of melanomacrophage centers in the splenic tissue and an increase in the amount of goblet cells in the gut. The concentration 108 CFU g-1 of probiotic in diets increased the number of goblet cells, improved cordonal aspects, and reduced hepatic congestion, and indicated a possible improvement in the immunophysiological conditions of the fish.
Keywords: Aquaculture; Fish health; Oreochromis niloticus; Sustainable fish farming.