Isolation of Edwardsiella tarda-like species and its frequency of occurrence in freshwater fish harvested for human consumption from Lake Hawassa and crater lakes around Bishoftu, Ethiopia

Abstract

A study was conducted to isolate Edwardsiella tarda-like species from apparently healthy freshwater fish 
(African cat fish, Clarias gariepinus and Nile tilapia, Oreochromis niloticus) originating from Lake Hawassa 
and crater lakes around Bishoftu, Ethiopia and thereby determine its distribution. Standard bacteriological 
examination of tissue specimens (kidney, liver and intestine) aseptically collected from fish harvested for 
human consumption resulted in a total of 16 isolates (10 from intestine, 4 from liver and 2 from kidney) 
showing similar colony and biochemical characteristics to E.tarda and were presumptively identified as 
E.tarda-like species due to the difficulties in differentiating them from the phenotypically similar new taxa 
viz. E.piscicida and E.anguillarum.  There was significant variation (P<0.05) in the chance of isolating the 
bacterium among the organs examined with the organism being most frequently isolated from the intestine. 
Of a total of 210 fish included in the study, the bacterium was isolated from 16 (7.6%) of them with significant 
difference (P<0.05) observed in its occurrence with respect to origin of fish host. The isolation of E.tarda-like 
species from apparently healthy fish in the current study indicates potential sources of disease epidemics in 
fish as well as safety concerns on local fish products consumed raw or improperly cooked.