The bacterial spoilage of four species of fresh fishes of commercial value namely Mackerel Sp, Synodontis schall, Clarias gariepinus (Cat fish) and Oreochronis niloticus (Tilapia) were investigated to determine the bacterial flora causing spoilage, as well as the spoilage pattern in the different fish species. Swabs of the body parts of the fishes were taken as inoculums and serially diluted in sterile distilled water, aliquot of the dilution were then plated onto nutrient agar medium. After incubation, the colonies were enumerated, Gram stained and subjected to biochemical characterization. Nine (9) genera of Bacteria namely Bacillus, Flavobacterium, Clostridium, Micrococcus, Pseudomonas, Staphylococcus, Streptococcus, Vibrio and Streptobacillus were isolated from the fish specimens and found to be responsible for spoilage. Mackerel had the highest bacteria count (5.90cfu/g) followed by Synodontis (5.78cfu/g) then Oreochromis niloticus (5.63cfu/g) and then Clarias gariepinus (5.55 cfu/g) which had the least. Only Bacillus and Micrococcus occurred all through in all the fish species investigated. The abdomen had the highest bacteria count then the head then the general body and then the tail which had the least.
Key words: Fish, Bacteria, Spoilage, Rigor mortis, Birnin Kebbi.