Tilapia Oreochromis niloticus is an aquaculture resource that represents one of the most popular crops in the world. However, species cultivation presents health problems, which are associated with the presence of pathogenic bacteria and causes high economic losses. The aim of this study was to determine the diversity of these bacteria at the genus level in the species O. niloticus var. Styrling during growing stage in the fattening and pre-fattening phases. Tilapia samples were collected and analyzed; each sample was subjected to a macroscopic external and internal observation of organs and tissues. Subsequently, samples were evaluated by microbiological tests using Trypticase Soy Agar (TSA), Thiosulfate Citrate Bile Salts Sucrose Agar (TCBS) and selective media (Pseudomonas sp. Group), and conventional biochemical tests aimed at the production of glucose, sucrose, lactose, oxidase, catalase, indole, ornithine and Gram staining. External analysis revealed clinical signs of disease such as skin bleeding, body ulceration, corneal opacity, and intestine and vesicle inflammation. Microbiological and biochemical analysis showed the presence of eleven bacterial genera known as Arthrobacter sp., Enterococcus sp., Staphylococcus sp., Micrococcus sp., Streptococcus sp., Aeromonas sp., Pseudomonas sp., Edwardsiella sp., Flexibacter sp. and Flavobacterium sp., with a predominance of 55% Gram-negative bacilli in tilapia crops. According to the results, it is necessary to take preventive and corrective measures in order to avoid possible risks during production cycles, mainly when handling organisms. It is also important to promote good crop management practices and quality systems in production units to benefit the aquaculture sector.

Edwardsiella tarda, Aeromonas spp., Vibrio spp., Francisella spp., Streptococcus agalactiae and S. iniae. Some of these pathogens are distributed throughout tropical and temperate regions where warmwater species, such as Nile tilapia, are commonly cultured. Merck Sharp and Dohme Corp. (MSD Animal Health) [2] mentions that mortalities increase with density (number of fish m-3) [3], and James et al. [4] and Bondad-Reantaso et al. [5] indicate that aquacultural health problems and the introduction of species promote the emergence of diseases. According to Snieszko [6], disease is related to the interaction between fish, pathogens and their waterways. When an organism is exposed to a bacterial pathogen in an unfavorable environment (e.g. poor water quality or excess of organic matter), disease incidence is higher because the balance between the pathogen, host and aquatic environment destabilizes. However, fish contain a high bacterial diversity, which results from a symbiotic effect among bacteria and tolerance by fish that protect them when adapting to nutritional changes and assimilation of food in the digestive tract [7].