Isolation and Antibiotic Susceptibility of Bacteria from Catfish (Clarias gariepinus) Sold in Aquaculture Markets in Oyo State

Aquaculture production of Clarias gariepinus has expanded substantially in Oyo State to meet protein demand in South West Nigeria, yet the microbiological safety of farmed catfish sold in markets remains poorly characterised. This study isolates bacteria from catfish sold in aquaculture markets in Oyo State and determines their antibiotic susceptibility profiles. Gill, gut, and muscle samples were collected from 60 live catfish purchased from five markets in Ibadan, Oyo, and Ogbomosho. Standard microbiological isolation on nutrient agar, MacConkey agar, and thiosulfate citrate bile salts sucrose agar was performed, with biochemical identification of isolates. Antibiotic susceptibility was determined by disk diffusion using 10 antibiotics. Aeromonas hydrophila, Escherichia coli, Salmonella species, and Vibrio species were the principal isolates. Aeromonas hydrophila was most prevalent in gill samples (68 percent), while Salmonella recovery from muscle tissues in 22 percent of fish is concerning from a food safety perspective. Resistance to tetracycline (77 percent) and ampicillin (82 percent) was high across isolates. Oxytetracycline resistance in Aeromonas isolates suggests prior therapeutic antibiotic use in aquaculture ponds. The study recommends restricted aquaculture antibiotic use, pre-sale bacteriological screening, and regulatory oversight of fish health management by the Oyo State Ministry of Agriculture and Rural Development. Keywords: catfish, Aeromonas hydrophila, antibiotic resistance, aquaculture, Oyo State