Monitoring of <i>Salmonella</i> spp. in Native Fish Farms in the Pantanal and Cerrado Biomes, Brazil: Serotype Diversity, Antimicrobial Resistance Profiles, and Multivatiate Patterns

ABSTRACT Mato Grosso State, Brazil, is the main producing region of native farmed round fish. This study aimed to investigate the occurrence of Salmonella spp. in fish farms located in the Pantanal and Cerrado biomes, across eight municipalities, focusing on the hybrid species tambatinga ( Colossoma macropomum × Piaractus brachypomus ); to analyze possible multicausal associations contributing to contamination during the fish farming phase; to characterize the circulating serotypes; and to assess the antimicrobial resistance profiles. A total of 184 samples were tested for Salmonella spp. following protocols from the International Organization for Standardization (ISO) and confirmed by polymerase chain reaction (PCR). Salmonella spp. was detected in 88% (22/25) of the fish farms and in 31.5% (58/184) of the samples. Contamination was confirmed in fish farms from all eight municipalities investigated, reinforcing the widespread circulation of the pathogen. Among the positive samples, 60.3% were from fish, with viscera showing the highest detection rate, while sediment/soil, pond water, and animal feces were the most frequent environmental sources. Serotyping revealed 10 distinct serotypes, with S . Saintpaul and S . Newport predominant, alongside S . Reading, S . Abaetetuba, and other less common serotypes of epidemiological relevance. The associations between environmental and management factors contributed to 57% of the explained variance in Salmonella spp. occurrence, and contamination was significantly higher during the dry season. Resistance was most frequent against azithromycin (44%) and sulfonamides (38%), although no multidrug‐resistant strains were identified. The high occurrence of Salmonella spp. during the fish farming phase demonstrates that associated factors contribute to contamination and the persistence of strains with resistance profiles from the early production stages. These findings highlight weaknesses in on‐farm biosecurity that must be addressed, while joint actions with good manufacturing practices in processing plants are also needed to mitigate risks. The circulation of diverse and epidemiologically relevant serotypes emphasizes the need for integrated surveillance under a One Health perspective in Brazilian aquaculture.