THE FOOD OF NON‐CICHLID FISHES IN THE LAKE VICTORIA BASIN, WITH REMARKS ON THEIR EVOLUTION AND ADAPTATION TO LACUSTRINE CONDITIONS

Abstract

The food of twenty‐six species of non‐cichlid fishes in the Lake Victoria basin is described. Most species, for which data were sufficient to show this, are facultative feeders, their food being determined by their size, their feeding grounds, and the age of the moon. The size of an organism and its position in the aquatic environment usually determine its importance as prey, and this is considered a reason why so many fishes in the lake are insectivorous. Only three species of non‐cichlid are extensively piscivorous: these feed heavily on Haplochromis, slightly on Engraulicypris, and hardly at all on Tilapia. Several birds and fishes feed on Engraulicypris, but otherwise there are few natural predators of non‐cichlids. Ontogenetic changes in feeding behaviour of Mormyrus kannume and Bagrus docmac support the hypothesis (recently confirmed for B. docmac) that in the lake juveniles of these two species live on rocky shores. The evolutionary stages involved in the colonization of lakes from rivers are discussed, with particular reference to breeding habits and food. The non‐cichlids in Lake Victoria are considered not to have progressed far towards becoming adapted to a lacustrine environment.