Análise da microbiota heterotrófica em alevinos de tilápia: impacto na sobrevivência e desenvolvimento durante a etapa de masculinização

Abstract

The intensification of aquaculture, especially tilapia farming, has driven the search for strategies to optimize production and disease prevention. The characterization of the intestinal microbiota of tilapia larvae revealed a complex and fundamental dynamic for fish health. The objective of this study was to monitor and characterize the succession and development of the bacterial community of Nile tilapia (Oreochromis niloticus), from hatching to the end of the masculinization stage, establishing its influence on the development and survival of the farmed animals. For microbiological characterization, quantification, isolation and antimicrobial susceptibility methodologies were applied. Zootechnical and limnological indices were also evaluated to monitor the culture parameters, as well as the evaluation of the sanitizing efficiency of the eggs collected with 4% formaldehyde. For this purpose, approximately 350 g of tilapia eggs were collected from a commercial farm located in the municipality of Cascavel/Ceará and taken to the Center for Coastal Environmental Studies (CEAC). The sanitation process was carried out with subsequent transfer of the eggs to the incubator and, after complete hatching, they were distributed to the cultivation units. The biometric and water quality parameters were measured periodically. A stocking density of 3 larvae/liter was used. The experiment lasted 28 days, with the animals fed commercial powdered feed containing 40% crude protein, added with 50% methyl-testosterone hormonal solution, at a feeding rate of 12% of the total biomass. Microbiological analyses were performed from the collection of the eggs, when two samples were collected for processing, one sanitized in formalin solution and the other without the solution. Then, four more microbiological processes were performed, distributed from the moment of complete hatching of the incubated eggs, at intervals of 7 days. The microbiological analyses were performed at the Laboratory of Environmental and Fish Microbiology – LAMAP/LABOMAR/UFC. The animals were properly euthanized by stunning in ice and eugenol solution. Cultivable heterotrophic bacteria were counted using the Standard Plate Count (SPC) technique, and isolations were performed based on growth. Then, the phenotypic characterization of the isolated strains was performed following the methodology proposed in Bergey’s Manual of Determinative Bacteriology. The disk diffusion test was used to perform the antibiogram, using 7 antimicrobials: Amoxicillin+clavulanic acid (20/10 µg), Aztreonam (30 µg), Enrofloxacin (5 µg), Streptomycin (10 µg), Gentamicin (30 µg), Norfloxacin (10 µg) and Tetracycline (30 µg). Throughout the culture, the physical and chemical parameters remained within the normal range for the species. The zootechnical results were also within the expected profile. Egg sanitation proved to be effective in reducing the external microbial load. The characterization of the microbiota revealed a dynamic microbial community, with a predominance of Enterobacteriaceae, Pseudomonadaceae, Vibrionaceae, Aeromonadaceae, Lactobacillaceae, Bacillaceae and Micrococcacea, respectively. The assessment of antimicrobial sensitivity revealed some percentage of resistance of the isolated strains, with the highest rates associated with Aztreonam (29.5%), Streptomycin (23.5%), Amoxicillin + clavulanic acid (23.5%). The results obtained highlight the importance of developing management and cultivation strategies in intensive systems.