STUDY ON BACTERIAL PATHOGENS OF FISH IN SOUTHERN GULF OF LAKE TANA WITH SPECIAL REFERENCE TO AEROMONAS HYDROPHILA AND EDWARDSIELLA TARDA
No Thumbnail Available
Date
2007-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A bacteriological study was conducted from September 2006 to March 2007 to estimate the occurrence and distribution of important Gram-negative bacteria with special reference to Aeromonas hydrophila and Edwardsiella tarda from the kidney and intestine of apparently healthy fish and their aquatic environment in the southern gulf of Lake Tana and carcasses of filleted fish (from commercial enterprises and local dealers) in Bahir Dar, Ethiopia. From a total of 510 swab samples taken from the kidney and intestine of 255 apparently healthy fish, different bacterial species, which belong to the family Aeromonadaceae, Vibrionaceae and Enterobacteriaceae were isolated and identified.
Among the isolates Aeromonas (A.) hydrophila (7.1%), Aeromonas (A.) caviae (9.8%), Aeromonas (A.) sobria (15%), Edwardsiella (E.) tarda (2%), Vibrio spp (7.8%), Yersinia (Y.) ruckeri (3.1%), Edwardsiella (E.) ictaluri (1.2%) and atypical strains of Aeromonas (A.) salmonicida (13%) were isolated in both the kidney and intestinal samples. Proteus (P.) mirabilis (5.9%), Enterobacter (E.) aerogenes (5.1%), Plesiomonas (P.) shigelloides (4.3%), Yersinia (Y.) enterocolitica (3.1%), Escherichia (E.) coli (2.4%), Klebsiella (K.) pneumoniae (2.4%), Proteus (P.) vulgaris (1.6%), Shigella (S.) sonnei (0.8%), Citrobacter (C.) diverses (0.4%) and Citrobacter (C.) freundii (0.4%) were isolated only from the intestine of fish. From carcasses of filleted fish A. sobria constituted 13.2% of the total isolates followed by A. caviae (9.6%), atypical strains of A. salmonicida (6.4%), Y. enterocolitica (4.8%), A. hydrophila (3.6%), E. coli (2.4%), P. mirabilis (1.6%), C. diverses (1.2%), P. shigelloides (1.2%) and Vibrio spp (0.8%).
Out of 62 water samples, 47 (75.8%) were positive for Aeromonadeceae and Enterobacteriaceae. All the bacterial species, which were isolated from the water samples, were also recovered from fish. Indicators of water pollution bacteria such as A. caviae and E. coli were more frequently isolated from sampling stations found in inshore littoral zone than stations found in sub-littoral and pelagic zones that are situated relatively far from the point source pollutions and hence less likely to be exposed to pollution.
XIII
From the results of the present study it was concluded that the intestine of fish have been found to be harboring a large group of bacterial species that may be a resident and/or transient microorganism. Isolation of similar types of bacteria from the fish, filleted fish and their aquatic environment has been recorded during the study period. The detection of similar bacterial species both in the fish and the water samples has some implications on the relationship between the fish and their aquatic environment (even though it requires some molecular characterizations of both isolates). Some of the bacterial isolates including Aeromonas hydrophila and Edwardsiella tarda are opportunistic pathogens of fish and may cause mortalities when the fish come under stress. Furthermore, the recovery of various organisms, which are potentially pathogenic to humans, in the kidney and alimentary tract of fish, and/or carcasses of filleted fish suggested that fish either improperly handled, undercooked or consumed raw might cause various diseases to susceptible individuals.
Description
Keywords
Aeromonadaceae, Vibrionaceae, Enterobacteriaceae, fish, kidney