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

Abstract

Parasites and bacterial pathogens of fish in Lake Ziway, Ethiopia, were studied during 1996-97. A total of 613 fish were sampled: 495 Nile tilapia (Oreochromis niloticus), 75 catfish (Clarias gariepinus), 24 Barbus sp., 11 Tilapia zillii and 8 carp species. They were thoroughly examined both externally and internally for the presence of parasites and lesions and samples were taken from a subset of the fish for bacteriological investigations. Among the bacteria, Edwardsiella tarda, (new geographic record) isolated from the liver of one O. niloticus and the kidney of a carp is known to be pathogenic to fish. On the other hand Shigella sp., Escherichia coli, Citrobacter, Klebsiella oxytoca, and Yersinia enterocolitica were the major bacteria identified from apparently healthy fish. Providencia alcalifaciens and P. stuartii were also present in some fish. The commonest parasite identified was Contracaecum sp. (metacercariae), found in 77 O. niloticus (15.6%), 3 T. zillii (27.3%), 4 C. gariepinus (5.3%) and 2 Barbus (8.3%). Clinostomum metacercariae were recovered from the branchial cavity of 45 O. niloticus (9.1%), 2 T. zillii (18.2%) and 3 C. gariepinus (4.0%). Only one Euclinostomum sp. metacercaria (new geographic record) was recovered from the branchial cavity of O. niloticus (0.2%). 13 C. gariepinus (17.3%) were carrying Amplicaecum metacercariae in their mesenteries and one (1.33%) was infected with Bothriocephalus sp.. The significance of these parasites and bacterial pathogens as causes of diseases in fish is discussed.