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The morphological and behavioural adaptations for feeding, and the food of C. gariepinus in Lake Sibaya are described. C. gariepinus is equipped to feed on a wide variety of food items, from minute crustaceans to fish. Predation is more efficient on invertebrate prey. Most feeding takes place at night on active benthic organisms, but they may also feed during the day and at the water surface. Individual bottom foraging is the normal mode of feeding although catfish may also feed in groups at the water surface. The advantages of social hunting are discussed.

Food preferences are scored by three different methods and presented for the total catfish population and for different length groups, seasons, habitats and lake levels. Increasing lake levels during the study period resulted in a change in the relative density of three cichlid prey in the shallow water feeding area of C. gariepinus. The effect of changing cichlid densities on catfish predation was studied using field collections and experimental observations. C. guriepinus was found to feed on whichever cichlid prey was in greatest abundance, with some deviations which can be explained in terms of prey accessibility and other factors. An important aspect of their success as predators is their ability to switch from one prey to another as prey availability (= density + accessibility) changes.

Predation by Clarias species on cichlids in Africa is reviewed, and the movements and interaction of C. gariepinus and three cichlid species in Lake Sibaya are described in detail. Catfish predation is discussed in terms of recent predation theory, and their role as predators of cichlids is tentatively postulated as three-fold:

  • (a) 
    to enhance species fitness by removing enfeebled individuals, i.e. to act as a “cleanser”
  • (b) 
    to restrict the distribution of prey under certain conditions, i.e. to act as a “restrictor”
  • (c) 
    to dampen fluctuations in prey abundance, i.e. to act as a “regulator”.
    The relative importance of these roles is unknown at this stage, and may change at different lake levels and in different ecosystems.