Comparison of the genetic and ecological diversity of the native to the introduced tilapiines (Pisces: Cichlidae), and their population structures in the Lake Victoria region, East Africa
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Date
2010
Journal Title
Journal ISSN
Volume Title
Publisher
Aquatic Ecosystem Health & Management
Abstract
The impact of introduced tilapiines in Lake Victoria Region (LVR) was studied using experimental
fishing survey methods and microsatellite DNA marker analysis. The experiments were carried out between
1993 and 2000. Oreochromis esculentus and O. variabilis, the two native forms of the LVR and original
principals of the fisheries of these waters, were found to be completely displaced from the major lakes
and were only occasionally found in a few minor satellite lakes surrounding Lakes Kyoga and Victoria.
Nile tilapia, O. niloticus, is now the dominant tilapiine, and one of the three key fisheries species of
LVR along with Nile perch, Lates niloticus, and the minnow-like Rastrineobola argentea. Oreochromis
leucostictus, also introduced to the LVR from the nilotic system, was largely restricted to swampy fringes of
LVR water bodies. Tilapia zillii, also introduced from nilotic waters and earlier recorded to have been the
most prevalent introduced tilapiine in LVR, occurred only sparsely and was very restricted in distribution.
Genetic studies showed Nile tilapia having the highest genetic diversity, and being the least subdivided
among LVR tilapiines. O. leucostictus was next in variability, but had the greatest gene flow, probably
due to its ability to traverse low oxygen waters such as swamps which separate most LVR water bodies.
The native forms were genetically the least variable, except where they coexist with introduced congeners.
‘Uncontaminated’ native forms were observed only in satellite Lakes of Kayanja, Kayugi, Manywa, Kawi
and Kanyaboli. The population structure of native forms of LVR suggest they are being genetically swamped,
especially for O. variabilis by Nile tilapia alleles, due to genetic exchange with introduced forms, resulting
in highly localized differentiation of native species. T. zillii was equally highly subdivided, but has higher
genetic variation within subpopulations, a situation linked to monogamous breeding behaviour which
allows most individuals of its population to participate in breeding. Hybridization with T. rendalli, which
was only occasionally encountered and previously mistaken for dwarf Nile tilapia, may also contribute to
high within population variation in small T. zillii populations. On a macro-evolutionary level, the sister
relationship between O. niloticus and O. esculentus is questionable and in need of further phylogenetic
analysis. Overall the study showed a changed fishery, and the need to manage satellite lakes in a manner
that will preserve the previous premier elements of the region’s fishery (O. esculentus and O. variabilis)
within natural refugia.
Description
Keywords
Oreochromis, Tilapia, Ecological displacement, Introgression, O. esculentus, O. variabilis
Citation
Mwanja, W. W., Kaufman, L., & Fuerst, P. A. (2010). Comparison of the genetic and ecological diversity of the native to the introduced tilapiines (Pisces: Cichlidae), and their population structures in the Lake Victoria region, East Africa. Aquatic Ecosystem Health & Management, 13(4), 442-450. DOI: 10.1080/14634988.2010.527268