Isolation, identification, and Koch’s postulate test of bacteria associated with yellow symptoms in african catfish Clarias gariepinus

Abstract

Farming african catfish Clarias sp at high stocking densities can foster stress and bacterial infection. In recent times, african catfish have frequently been discovered displaying symptoms of yellow body jaundice, often resulting in mass mortality. The objective of this study was to identify and characterize bacteria linked to jaundice in african catfish. Bacterial isolates were obtained from ten african catfish with yellowish body symptoms, identifying six dominant isolates. Bacteria were examined for Koch’s postulates by injecting 0.1 mL of bacteria, with a concentration of 106 CFU mL-1, into african catfish measuring 21.6±1.7 cm in length. The results of the infection test revealed that fish injected with the six bacterial isolates exhibited pathogenic symptoms, including pale body coloration, dropsy, reduced active swimming, fin thinning, ulceration, and mortality. These symptoms indicate that the bacteria are pathogenic to catfish. The study revealed that six bacterial strains were discovered in the internal organs of jaundiced african catfish. These strains were identified as Staphylococcus pasteuri, Salmonella enterica, Escherichia coli, Enterobacter hormaechei, Bacillales bacterium, and Aeromonas salmonicida. The result suggest the presence of bacteria associated with jaundice in african catfish. The outcomes of the Koch’s postulate test indicate that the infection of fish with less specific symptons of illness can lead to jaundice.