Ecological Segregation in Zooplanktivorous Haplochromine Species (Pisces: Cichlidae) from Lake Victoria

Until a few years ago, Lake Victoria possessed a large species flock of haplochromine cichlids, comprised of 250+ species. Very little was known about the possible ecological differentiation within trophic groups, and virtually nothing about the mechanisms structuring the community. This paper deals with zooplanktivorous species from the Mwanza Gulf of Lake Victoria that showed a large overlap in gross morphological characteristics. We found strong evidence that the species were ecologically segregated to a great extent. Species were restricted to certain horizontal and/or vertical zones. Species which segregated relatively little horizontally, did so vertically, and/or by different diet. The two species with the largest diet overlap segregated vertically. Species pairs segregated along at least one of the traditional niche axes: space, food and time. A detailed study of vertical distributions did not yield any evidence for interactive competition for space. Vertical distributions of fish and food at a 14 m deep station correlated well by night. By day the concordance was less clear.