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Edwardsiellosis is a very common fish disease in framed fish caused by Edwardsiella tarda which can lead a severe economic loss in aquaculture worldwide. Isolation and identification of the pathogenic bacteria Edwardsiella tarda from three fish species: catla Catla catla, koi Anabus testudineus and tilapia Tilapia mosumbicus were undertaken from different area of Mymensingh District. The intestine, liver and kidney of each fish were inoculated into Salmonella-Shigella (SS) plates and TSA plates. The colonies of the SS plates were subcultured onto TSA plates and undergone specific identification processes through their morphological and biochemical tests for Edwardsiella tarda. They were Gram negative, rod shaped, motile, oxidase negative bacteria that showed positive reactions for catalase and fermented glucose. Quantitative studies of the bacterial flora of the above fishes on TSA plates showed that the minimum total bacterial load of tilapia was 1.50 × 102 cfu/g in the blood and the maximum was 8.20 × 106 cfu/g in kidney. In case of catla, the minimum load was 2.36 × 103 cfu/g in the blood and the maximum was 8.20 × 106cfu/g in intestine. Koi showed its minimum load of 2.45 × 103 cfu/g in the blood and a maximum of 5.54 × 105 cfu/g in liver. It was understood that the bacteria Edwardsiella tarda is an opportunistic pathogen in Bangladesh aquaculture and can, any time be a cause of serious disease condition of culture fishes of Bangladesh at least in catla, koi and tilapia.
Alam et al. (Sat,) studied this question.