Histological effects on the kidney, spleen, and liver of Nile tilapia Oreochromis niloticus fed different concentrations of probiotic Lactobacillus plantarum.

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.

Autochthonous vs allochthonous probiotic strains to Rhamdia quelen.

The aim of this study was to obtain an autochthonous probiotic candidate strain from the silver catfish (Rhamdia quelen) intestinal tract, comparing its in vivo performance with an allochthonous probiotic isolated from another fish, Nile tilapia (Oreochromis niloticus), in a growth performance assay. The study was divided in two parts: in vitro and in vivo assay followed by challenge with A. hydrophila. In the in vitro assay, the species-specific isolated strain Lactococcus lactis presented characteristics such as: absence of hemolysis, antagonism to bacterial pathogens isolated from freshwater fish, and considerable speed of duplication. In the in vivo trial, both fish supplemented with autochthonous or allochthonous strains presented an increase the final concentration of lactic acid bacteria in the intestinal tract of the fish after 60 days of dietary supplementation reaching concentrations of 1 × 107 CFU g-1 and 4 × 107 UFC.g-1, respectively. In addition, the autochthonous strain increased the mean corpuscular hemoglobin (MCH) of the treated animals, but no significant differences were observed in the other hemato-immunological and zootechnical parameters between treatments. After challenge with Aeromonas hydrophila, only animals that received autochthonous probiotic supplementation showed an increase in the serum total immunoglobulin concentration, but not enough to observe a significant difference in the survival rate between the treatments. Dietary supplementation of the probiotic allochthonous strain did not demonstrate any effects superior to those of the isolated autochthonous strain. Although the autochthonous strain did not present significant improvements in the other parameters evaluated in this study, it was able to inhibit bacterial pathogens in vitro, to increase the final concentration of LAB's and the amount of immunoglobulin after experimental challenge, demonstrating probiotic potential. This study demonstrated for the first time the isolation and in vivo use of an autochthonous probiotic strain isolated from silver catfish, as well as its comparative evaluation with the performance of allochthonous probiotic.