Potential Biological Control of Schistosomiasis by Fishes in the Lower Senegal River Basin

Abstract

More than 200 million people in sub-Saharan Africa are infected with schistosome parasites. Transmission of schistosomiasis occurs when people come into contact with larval schistosomes emitted from freshwater snails in the aquatic environment. Thus, controlling snails through augmenting or restoring their natural enemies, such as native predators and competitors, could offer sustainable control for this human disease. Fishes may reduce schistosomiasis transmission directly, by preying on snails or parasites, or indirectly, by competing with snails for food or by reducing availability of macrophyte habitat (i.e., aquatic plants) where snails feed and reproduce. To identify fishes that might serve as native biological control agents for schistosomiasis in the lower Senegal River basin-one of the highest transmission areas for human schistosomiasis globally-we surveyed the freshwater fish that inhabit shallow, nearshore habitats and conducted multivariate analyses with quantitative diet data for each of the fish species encountered. Ten of the 16 fish species we encountered exhibited diets that may result in direct (predation) and/or indirect (food competition and habitat removal) control of snails. Fish abundance was low, suggesting limited effects on schistosomiasis transmission by the contemporary fish community in the lower Senegal River basin in the wild. Here, we highlight some native species-such as tilapia, West African lungfish, and freshwater prawns-that could be aquacultured for local-scale biological control of schistosomiasis transmission.

Figure 1.

Map of the study region in the lower Senegal River basin. Bodies of (fresh and marine) water are noted in dark grey. International and regional boundaries are indicated by dashed lines. This figure appears in color at www.ajtmh.org.

Figure 2.

Rarefaction curve of observed fish species. Interpolation of observed species (solid line), extrapolation to 500 individuals (dashed line), and 95% confidence interval (faded red) are included. Genera in which we could not identify any specimens to the species level (Chrysichthys, Clarias, and Labeo) were each treated as a single species. For genera in which we could not identify a subset of the specimens to the species level (Polypterus, Synodontis), we included only those specimens that were explicitly assigned a species name. Thus, the sample size reflected in this figure is less than that presented in Table 1. This figure appears in color at www.ajtmh.org.

Figure 3.

Dietary niche breadth estimated from the available diet composition literature of each species/genus observed in this study. Species/genera are ordered from least (top) to greatest (bottom) dietary niche breadth. Error bars represent 95% confidence intervals. Species estimated from less than three datasets do not have error bars. Genera level estimates are calculated from datasets for native species of that genus (see Methods: Dietary Niches).