Abstract
This study developed niche models for the native ranges of Oreochromis andersonii, O. mortimeri, and O. mossambicus, and assessed how much of their range is climatically suitable for the establishment of O. niloticus, and then reviewed the conservation implications for indigenous congenerics as a result of overlap with O. niloticus based on documented congeneric interactions. The predicted potential geographical range of O. niloticus reveals a broad climatic suitability over most of southern Africa and overlaps with all the endemic congenerics. This is of major conservation concern because six of the eight river systems predicted to be suitable for O. niloticus have already been invaded and now support established populations. Oreochromis niloticus has been implicated in reducing the abundance of indigenous species through competitive exclusion and hybridisation. Despite these well-documented adverse ecological effects, O. niloticus remains one of the most widely cultured and propagated fish species in aquaculture and stock enhancements in the southern Africa sub-region. Aquaculture is perceived as a means of protein security, poverty alleviation, and economic development and, as such, any future decisions on its introduction will be based on the trade-off between socio-economic benefits and potential adverse ecological effects.
Highlights
Nile tilapia, Oreochromis niloticus (Linnaeus 1758), is an endemic African freshwater cichlid that is native to the Nile River basin, southwestern Middle East, and the Niger, Benue, Volta, and Senegal rivers, as well as lakes Chad, Tanganyika, Albert, Edward, and Kivu [1,2]
(2) we investigated the degree of niche overlap between the projected invasive range of O. niloticus and the natural ranges of endemic congenerics in river systems in southern Africa, and reviewed the conservation implications for indigenous congenerics as a result of overlap with O. niloticus based on documented congeneric interactions
The native ranges of all three tilapia species (O. andersonii, O. mortimeri, and O. mossambicus) that are endemic to southern Africa were correctly predicted with good model performance
Summary
Oreochromis niloticus (Linnaeus 1758), is an endemic African freshwater cichlid that is native to the Nile River basin, southwestern Middle East, and the Niger, Benue, Volta, and Senegal rivers, as well as lakes Chad, Tanganyika, Albert, Edward, and Kivu [1,2]. Owing to its hardy nature, and its wide range of trophic and ecological adaptations, O. niloticus has been widely introduced worldwide for aquaculture, augmentation of capture fisheries, and sport fishing [1,3]. Within sub-Saharan Africa, O. niloticus was initially introduced into Lake Victoria in the 1950s and its distribution has since expanded to include most river systems in eastern and southern Africa [6] It was imported into Zambia in 1982 for aquaculture purposes and appeared in the Kafue River in the mid-1990s after escaping from nearby fish farms [7].
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