Genetic impacts of fish introductions: a perspective on African lakes

Abstract

The conflict between the demand for short-term benefits in fisheries yield and the long-term conservation of biodiversity is nowhere more apparent than in African fresh waters. Artificial changes in African fresh waters through habitat destruction or exploitation have led to a marked reduction in the diversity and abundance of many fish species, some of which have become extinct before being fully described. It is through fish introductions, however that some of the most alarming impacts on biodiversity have occurred. The rapid and direct effects of such perturbations on the population genetic structure of alien or native species through microevolutionary forces has led to extensive species changes. The great concern is that once initiated, a reduction in genetic variability, or introgression between species will persist over an evolutionary time scale and may therefore be irreversible in the short term. Conservation of genetic resources must include not only practices that minimize loss of genetic diversity, but also measures to preserve the associated genotypic variance in ecologically significant traits. It is the ultimate phenotypic expression of genotypic variability in viability and fecundity that will determine the adaptability and persistence of local populations and thus the evolutionary potential of a species. Future research priorities should include genetic studies on the extent and consequences of hybridization, as well as a description of temporal and spatial patterns in genetic variability.