News
 

Researchers predict the invasive potential of Nile tilapia

Invasive aquatic species, once established, are virtually impossible to eradicate. As is often the case with highly invasive fish species, after their establishment, the only practical management option is to predict the speciesí eventual distributional range and adopt measures to either stop or slow its spread across river systems. Ecological niche models are effective tools for predicting the potential range of invasive species, and directing management efforts.

In a paper published in Biological Invasions, C·I·B researchers made use of ecological niche models to determine the potential invasive range of Nile tilapia, Oreochromis niloticus in southern Africa rivers systems. The authors evaluated the differences in the predictive power of models trained with different environmental conditions, the effect of using species native vs introduced range on model performance and assessed whether or not there is evidence suggestive of a niche shift in Nile tilapia following its introduction. The environmental variables dataset was composed of proxy bioclimatic variables that represent annual trends (mean annual temperature and annual precipitation), seasonality (annual range in temperature and precipitation) and either extreme or limiting environmental factors (temperature of the coldest and warmest months and precipitation of the wet and dry quarters).

Results indicated that the number and type of environmental variables influenced the projected native and introduced ranges of Nile tilapia and that the environmental conditions available to Nile tilapia in its native and introduced ranges are not similar.

The major conservation implication from this study was that a large proportion of river systems in southern Africa offer suitable habitats/conditions for the establishment of Nile tilapia. Nile tilapia showed a broad invasive potential over most of southern Africa that overlaps the natural range of all six endemic congenerics. The localised distribution of these six endemic congenerics predisposes them to invasion because the introduction of Nile tilapia into a given catchment is likely to have a significant impact on species that have limited natural ranges. The advent of Nile tilapia into these river systems is a cause for concern for the conservation of indigenous congenerics that are at risk of extirpation through hybridization and competition with Nile tilapia as observed elsewhere in systems where this species has been introduced. Of particular concern are those areas that have been free of non-native species but were predicted to be potentially suitable for the establishment of Nile tilapia and are now vulnerable due to the promotion of aquaculture and sport fishing. These areas currently act as “reserves” for the conservation of indigenous congenerics and intensive conservation efforts should be implemented to keep them free of invasive species.

Tilapiine habitat, Limpopo River

Typical tilapiine habitat, Limpopo River, South Africa




Read the paper

Zengeya TA, Robertson MP, Booth AJ, Bastos ADS, Chimimba C.T. (2012). Ecological niche modeling of the invasive potential of Nile tilapia, Oreochromis niloticus in African river systems: concerns and implications for the conservation of indigenous congenerics. Biological Invasions DOI 10.1007/s10530-012-0386-7

For further details, contact Chris Chimimba at ctchimimba@zoology.up.ac.za.