Feeding performance of Lake Victoria rock cichlids: testing predictions from morphology

Cichlid fishes that seem specialized phenotypically to exploit certain resources often act as generalists in the held. It is attempted to resolve this paradox by measuring feeding performance. There are two ways of feeding, namely suction feeding and biting, that set conflicitng demands on the anatomy. Rock-dwelling cichlids of the genus Neochromis are specialized biters, feeding largely on filamentous algae and benthic organisms. Pundamilia nyererei is one of the most specialized suction feeders among rock cichlids, its diet being zooplankton and insect larvae. A morphological analysis showed that the three Neochromis species are better adapted anatomically to biting than P. nyererei, while P. nyereiei is better adapted to suction feeding. Feeding performance was tested on algal substitute and Chaoborus larvae, representing filamentous algae and zooplankton, respectively. As expected the Neochromis species fed most efficiently on algal substitute, N. rufocaudalis and N. omnicaeruleus taking per bite 2.6 times as much as P. nyereiei, and N. greenwoodi 1.7 times. Unexpectedly, the species examined were all well able to collect Chaoborus. P. nyereiei collected only 1.2 limes as many larvae per suction act as the Neochromis species. Analysis of the stomach contents showed that P. nyereiei punctured, or lacerated, the larvae with the pharyngeal jaws, while the Neochromis species swallowed them mostly intact. Thus, feeding on Chaoborus, P. nyererei may be optimizing energy gain and not intake rate. (C) 1998 The Fisheries Society of the British Isles.