Search

Streptococcus agalactiae is a highly invasive bacterium that causes significant economic losses in tilapia aquaculture around the world. Furthermore, it is a pathogen for mammals, including humans, emphasizing its importance in One Health. The aim of this work was to evaluate the evolution of clinical and histopathological lesions caused by acute infection with two serotypes of S. agalactiae. For this, two strains isolated from natural outbreaks in Brazilian aquaculture farms (S13, serotype Ib; S73, serotype III) were used to challenge juvenile Nile tilapia (Oreochromis niloticus) intraperitoneally. Target organ samples were collected ten times, between 1 and 96 h post-infection, for microbiological and histopathological analyses. Anorexia was the first clinical sign and the first death occurred at 24 and 30 h in the fish infected with strains S13 and S73, respectively. Serotype Ib initially caused more pronounced lesions in the nervous system; however, serotype III lesions progressed more aggressively, reaching the same severity as those of serotype Ib. This trend was repeated in the mortality curve after 32 h. These results elucidated the important stages in the pathogenesis of S. agalactiae serotypes Ib and III in tilapia and suggest “tips and tricks” to improve the positive culture rate in the clinical diagnosis of infections in some tissues.

The great commercial potential of Nile tilapia is due to features such as its high production performance, its adaptability to different farming systems, and the development of genetic varieties with superior performance. Therefore, the objective of this study was to evaluate the performance of two varieties, GIFT (Genetic Improvement of Farmed Tilapia) and Supreme, grown in hapas in concrete tanks and grown in excavated ponds. Were used 200 and 1234 fingerlings of both varieties, GIFT and Supreme (average initial weight of 0.83 g), for farming in hapas and ponds, respectively. Biometric measurements were taken at four farming stages (fingerling, juvenile, growth, and fattening). Were measured weight (g), total length (cm), standard length (cm), trunk length (cm), head length (cm), head height (cm), body height (cm), weight gain (g) and head/edible-part ratio. For all parameters and in all stages, superior results were observed for tilapia reared in excavated ponds. When the varieties were compared, GIFT had the best performance for most parameters in the fingerling stage, and for weight, total length, and body height in the juvenile stage. Both varieties grew better in excavated ponds. Moreover, GIFT showed higher growth than Supreme during all stages when grown in excavated ponds. Supreme showed higher growth than GIFT in hapas only in the growth stage. Thus, it is concluded that the rearing in excavated ponds provided better results, with superiority of the GIFT variety, which was more able to take advantage of the favorable conditions of this system.

Nutritional improvements in intensive aquaculture production systems is necessary for the reduction of stress, maximum utilization of nutritional components, and expression of the genetic potential of fish. The objective of this study was to evaluate the hemato-immunological, and histological parameters and gut microbiota of Nile tilapia fed with the microalga Schizochytrium sp. Males of Nile tilapia were distributed among eight net cages (6 m3), and fed for 105 days with two diets: control (CON), without Schizochytrium sp., and supplemented (SUP), with 1.2% Schizochytrium sp. in the diet. The final weight, mortality, hematocrit, total erythrocyte count (RBC), hemoglobin, hematimetric indices, white blood cell count (WBC), total protein, and serum lysozyme were measured. Alterations in intestinal morphology were evaluated. The gut microbiota was evaluated with next-generation sequencing. No significant differences (p>0.05) were found in the final weight and mortality between diets. Regarding the hematological parameters, a difference (p0.05) in total protein and serum lysozyme concentrations or in WBCs between diets, except for lymphocytes, which presented lower values (p0.05) in the intestinal morphology between diets. Metagenomic data indicated greater richness (represented by the Chao index) and a higher abundance of the bacterial phylum Firmicutes in the gut microbiota of the tilapia fed with the SUP diet, demonstrating that the digestion and use of the components of the microalga could influence the microbial community. The results indicated that the microalga had modulatory effects on blood cells and the intestinal microbiota, without affecting the structure and integrity of the intestinal villi.