NOTE ON THE OCCURRENCE OF A VENTRAL SUCKER-LIKE MOUTH FORM IN LABEO UMBRATUS (PISCES, CYPRINIDAE)

Abstract

The occurrence of a ventral sucker-like mouth form in certain populations of Labeo umbratus, which are free from competition by L. aapensis, is reported. It is proposed that this might be an adaptation to feeding off stones which enhances the fish's changes of survival. If this is so, the absense of mouth form variation in Orange River populations illustrates the force of interspecific competition with L. capensis.