Diet of the cyprinid fish Barbus aeneus (Burchell) in the P.K. le Roux Dam, South Africa, with special reference to the effect of turbidity on zooplanktivory

Abstract

Barbus aeneus is one of the most important fishes in the P.K. le Roux Dam, being found over the whole surface and on the bottom down to the thermocline or to 30 m. It is omnivorous, but its diet varies with size. Below a length of 100 mm it feeds mainly on zoobenthos, from 101 - 300 mm zooplankton is the principal food but in larger fish vegetable food becomes increasingly important. B. aeneus is the principal vertebrate consumer of zooplankton in the dam, but takes only the larger species which are located visually. The quantity of zooplankton in the diet was related, not to its density, but to light and transparency which were the most important non-seasonal influences on the diet. Seasonal effects were marked, zooplankton being most important during summer and autumn while empty stomachs were most frequent in winter and spring. In rivers, larger B. aeneus feed on bigger invertebrates and on vegetable material. These are limited in the P.K. le Roux Dam and sub-adults experience high mortality once they can no longer feed efficiently on zooplankton. The size at which this occurs is determined largely by turbidity, and this should be taken into consideration in formulating management policies.