Body shape differences between two benthophagous, sympatric cichlid species,
Ctenopharynx pictus and Otopharynx sp. "heterodon nankhumba" were examined
for 14 morphometric characters using measurements obtained from 11 morphological landmarks
and additional 6 characters from the head region using principal component and regression
analyses. The two species, though not closely related, superficially resemble each other
and, being benthic feeders, directly compete for food resources unless morphological
differences lead to trophic specialization. Hence, the present study explores the presence
of such morphological variations. Principal component analysis (PCA), revealed that only
four characters loaded highly on PC II and, therefore, account for most of the variations
in the external morphology between the two species. C. pictus has longer lower jaws
reflecting longer gape, and a shorter abdominal cavity than O. sp. "heterodon nankhumba".
The regression analyses showed significant differences in the allometric coefficients of the
lower jaw and abdominal cavity, which might have contributed to differences in overall shape
detected between the two species. The difference in gape size between the two species may be
related to different feeding habits employed by each species, and such specializations are
suggested to reduce interspecific competition for food resources. We suggest that the ensuing
ecological separation promotes sympatry of these two species.