Kibru Teshome , Adamneh Dagne , Fasil Degefu , Mareshet Adugna

Ethiopian Institute of Agricultural Research, National Fisheries and Aquatic Life Research Center, P.O. Box 64 Sebeta, Ethiopia
Author    Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 24   doi: 10.5376/ija.2014.04.0024
Received: 28 Aug., 2014    Accepted: 21 Sep., 2014    Published: 27 Oct., 2014

This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Teshome et al., 2014, Selective predisposition of Nile tilapia (Oreochromis niloticus L.) to bacterial and parasitic infection- evidence from the crater lakes Babogaya and Hora-Arsedi, Ethiopia, International Journal of Aquaculture, Vol.4, No.24: 1-8 (doi: 10.5376/ija.2014.04.0024)

Mass mortalities of fish sporadically occur throughout the globe and often caused by single or multiple factors posing difficulties on the search for plausible explanations. Following the selective mass mortality of Oreochromis niloticus in two of the Bishoftu Crater Lakes: Babogaya, and Hora-Arsedi between April and May of 2013, we carried out a snapshot survey on the limnology of Lakes Babogaya and Hora-Arsedi including the histopathological and bacteriological examinations of O. niloticus fish. Complete mixing of the lake water and the subsequent anoxic condition was primarily hypothesized as the likely cause. However, vertical, profile of water temperatures and dissolved oxygen concentrations revealed that both lakes were stratified and the epilimnion was well oxygenated (> 8.9 mg L^-1). All key water quality parameters were within the optimum range for O. niloticus culture except ammonia which was well above the lethal level (2.1 mg L^-1) in Babogaya and stressive sublethal level of 0.1mg L^-1 in Hora-Arsedi. Live fish samples showed clinical symptoms such as caudal skin lesion and injured gills. Postmortem examinations revealed hemorrhagic shock, liver and kidney damage with Aeromonas sp. and parasitic infections detected. Therefore we concluded that direct ammonia toxicity have caused the mortalities in Lake Babogaya, whilst extended sublethal ammonia exposure with subsequent stress and gill damage predisposed the fish to bacterial and parasitic infection that led to mass mortalities in Lake Hora-Arsedi.

Ammonia; Oreochromis niloticus; Fish kill; Mass mortality; Lake Babogaya; Lake Hora-Arsedi