Preliminary survey of parasites and bacterial pathogens of fish at Lake Ziway

Abstract

Parasites and bacterial pathogens of fish at Lake Ziway, during 1996B97 were studied. A total of 613 fish were sampled. These included 495 Nile tilapia (Oreochromis niloticus), 75 Catfish (Clarias gariepinus), 24 Barbus species, 11 Tilapia zillii and 8 carp species. The fish were thoroughly examined both externally and internally for the presence of parasites and lesions and samples were taken for bacteriological investigations. Among the bacteria, Edwardsiella tarda, (new geographic record) isolated from the liver of one O. niloticus and kidney of another carp species is known to be pathogenic to fish. On the other hand Shigella species, Escherichia coli, Citrobacter, Klebsiella oxytoca, and Yersinia enterocolitica were the major bacteria identified from the apparently healthy fish. The major parasites identified included Contracaecum species from 77 (15.56 %) of O. niloticus, 3 (27.27%) T. zillii, 4 (5.33%) C. gariepinus and 2 (8.33%) Barbus species. Clinostomum species were recovered from the branchial cavity of 45 (9.09%) Oreochromis niloticus, 2 (18.18%) Tilapia zillii and 3 (4.00%) C. gariepinus. Only 1 Euclinostomum species (new geographic record) was recovered from the branchial cavity of O. niloticus. Moreover 13 (17.33%) C. gariepinus were carrying Amplicaecum species in their mesentery and one C. gariepinus was positive to Bothriocephalus species. The significance of these parasites and bacterial pathogens as causes of diseases to fish is discussed. SINET: Ethiopian Journal of Science Vol. 23, No. 1 (June 2000), pp. 25-33 Key words/phrases: Bacteria, Edwardsiella tarda, fish diseases, Lake Ziway, parasites