Interdemic variation in the foraging ecology of the African cyprinid, Barbus neumayeri

In the African cyprinid, Barbus neumayeri, populations from hypoxic waters have larger gills than populations from well-oxygenated streams. Differences in trophic morphology and feeding performance between these populations suggest a reduction in feeding efficiency in large-gilled fish that may reflect spatial constraints of the gills. However, this variation may also reflect interdemic variation in diets. In this study, we describe patterns of variation in diet, gut morphology, and prey availability for populations of B. neumayeri from swamp (low-oxygen) and stream (high-oxygen) sites in Kibale National Park, Uganda. Our results indicate that B. neumayeri are omnivorous, feeding primarily on benthic prey items; however, diets differed among swamp and stream sites for certain prey types. The observed dietary differences do not provide direct support for predictions based on variation in trophic musculature; hard-bodied prey were more common in low-oxygen sites. Prey availability also differed among sites; in particular, insect abundance and richness was generally lower in the swamp sites. Gut length was longer in one of the four populations, but did not conform to expectations based on diet differences. Condition and growth rates did not differ between populations from hypoxic and well-oxygenated sites, despite observed differences in prey availability and diet, suggesting that B. neumayeri may be distributed in a way that equalizes fitness among populations in different habitats.