The ecology of two commercially important catfish species, Clarias gariepinus and C. ngamensis, was examined in the Elephant Marsh, southern Malawi. Abundance, distribution, and movements within the marsh system were studied. Growth rates were determined from rings on the vertebrae, with corroborative evidence from length frequency analyses and tagging studies. Breeding seasons, length and age at maturity, and fecundity were determined for both species. Stomach contents were examined and the food preferences of the two species were compared.