TROPHIC INTERRELATIONSHIPS AMONGST CICHLID FISHES IN A TROPICAL AFRICAN RESERVOIR (LAKE CHIVERO, ZIMBABWE) By

i The diet of seven cichlid fish species of Lake Chivero was investigated from October 2004 to April 2005. Oreochromis niloticus and O. macrochir were microphages feeding on a wide range of algae of which Microcystis sp., made up>50 % of their diet, while the rest of the food items were chlorophytes, diatoms, zooplankton, insects and detritus. Tilapia sparrmanii and T. rendalli were primarily macrophages consuming plant material and filamentous algae, but also fed on diatoms and zooplankton. The small species P. acuticeps and P. philander had a catholic diet comprising of algae, zooplankton, plant material, fish and detritus. Serranochromis robustus was a carnivore and fed mainly on fish. They were no ontogenetic diet shift for all species except for S. robustus and P. acuticeps. Diet shift occurred at 50mm SL, were the major food item in the diet of small < 50mm size classes was zooplankton whereas the larger fish included a wider range of food items in their diet. Dietary overlap was low and insignificant in most species, except for O. macrochir/P. philander and T. sparrmanii/P. philander in the 51-100mm size-class and O. niloticus and O. macrochir among the larger fish species (>100 mm). Competition among the small species and the juveniles of the large species may be reduced by abundant food resources, habitat preferences, ontogenetic diet and habitat shifts. Direct competition between O. niloticus and O. macrochir may result in the exclusion of the latter.The cichlid species in the lake were grouped into three major feeding group microphages, macrophages and carnivores and omnivores. These feeding guilds utilise most of the available food niches in the lake, except for zoo benthos and gastropods. i