The fish communities of the rocky littoral zone of Lake Malawi contain a large number
of ecologically similar cichlid species. It has been suggested that dietary niche
segregation may play a role in the coexistence of these species, but previous studies
have yielded ambiguous results. Stable isotope analysis was used to determine whether
five sympatric species are segregated by diet. Significant differences were found
between the mean isotopic signatures of the study species, but there was considerable
interspecific overlap between three species from the same subgenus that were
anatomically almost indistinguishable. The implication that this was due to substantial
dietary similarity was supported by stomach content analysis. We propose that ecological
segregation may not always be necessary to allow coexistence of Lake Malawi cichlids.