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International Journal of Aquaculture, 2014, Vol.4, No.24, 1
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8
http://ija.biopublisher.ca
1
Research Article Open Access
Selective predisposition of Nile tilapia (
Oreochromis niloticus
L.) to bacterial and
parasitic infection- evidence from the crater lakes Babogaya and Hora-Arsedi,
Ethiopia
Kibru Teshome, Adamneh Dagne, Fasil Degefu , Marshet Adugna
Ethiopian Institute of Agricultural Research, National Fisheries and Aquatic Life Research Center, P.O. Box 64 Sebeta, Ethiopia
Corresponding author Email
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
Copyright © 2014
Teshome et al., 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.
Preferred citation for this article
:
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
Abstract
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.
Keywords
Ammonia;
Oreochromis niloticus
; Fish kill; Mass mortality; Lake Babogaya; Lake Hora-Arsedi
Introduction
Natural fish mortality is often caused by several
factors such as aging, sporadic diseases and genetic
deformity among populations which involves
individual fish at any age and often not easily
recognizable. However, in events of mass mortality of
fish, large number of individuals suddenly die off at
the same time in a localized area that a passersby can
easily spot (Meyer and Barclay, 1990; Lugg, 2000).
Such mass fish kills are often caused by factors other
than those which cause natural mortality. Mass fish
kill sporadically occurs in many water bodies around
the globe. For instance several fish kill outbreaks
occurred in 2005 in which three peaks of mortality at
an interval of one month were recorded in Northern
Europe (Castro et al
,
2006). Similar evidence of mass
fish kill has also been reported recently from Lake
Hayq in northern Ethiopia (Fetahi et al, 2011).
Nevertheless, mass fish mortality cases are often not
sufficiently investigated in developing countries like
Ethiopia due to technical difficulties associated with
parameters that cannot be controlled during the events.
Results are often not conclusive and in most cases
multiple factors are responsible for mass mortalities
(La and Cooke, 2011). Seldom, sudden mass fish kills
are associated with single traceable causes such as
pollution of aquatic environments with toxic
substances from industries (Abdelaziz, 2010), high
fluxes of volcanic gases such as CO
2
and H
2
S from the
hypolimnion of crater lakes (Kling, 1988; Löhr et al,
2005), decays of toxic algal bloom (Challappa et al,
2008) and hypoxia caused by eutrophication and
nutrient resuspension from the sediment (Wetzel,
2001). Virulent bacterial strains of the motile
Aeromonas
sp.
,
Edwardsiella
sp. and
Flexibactor
columnaris
are also known to cause significant
mortalities both in culture and wild populations of
warm water species (Amin et al, 1988; Mohanty and
Sahoo, 2007). A number of other factors such as
bacterial, fungal and parasitic disease outbreaks have