Feeding habits of the catfish Synodontis schall (Bloch & Schneider) (Pisces: Mochokidae) with emphasis on its scale-eating habits in Lake Chamo, Ethiopia

Abstract

Synodontis schall (Bloch & Schneider) is an abundant fish in Lake Chamo, but its feeding ecology is not well-known to guide its management. Diet composition and ontogenetic diet shift were investigated from stomach contents of 545 fish from August 1998 to February 2000. Volumetrically, the dominant food items were zooplankton, fish scales and macrophytes. Zooplankton occurred in 83.3% of the stomachs and accounted for 26.5% of the total volume. Fish scales occurred in 35.0% of the stomachs and accounted for 30.6% of the total volume of food. Macrophytes occurred in 9.8% of the stomachs and contributed 19.4% of the total volume of food eaten. Insects occurred in 37.3% of the stomachs and contributed 8.3% of the total volume of food eaten. Fish fry occurred in 13.7% of the stomachs and constituted 10.9% of the total volume of food consumed. Diatoms, zooplankton and insects constituted 89.8% of the volume of food eaten by juveniles, but their importance declined with the size of fish. Importance of fish scales increased with size of fish. From these results, it is evident that zooplankton and insects were the most important food items of juveniles while fish scales, fish fry and macrophytes were the most important food items of adults. The information obtained from this study allows us to determine the effect Synodontis has on other organisms through competition and predation. This knowledge can be used in management of Synodontis fisheries by determining the prey type of the species and how the changing biological and physical conditions in the lake affect them.

Key words/phrases: Ethiopia, Feeding, Lake Chamo, Synodontis schall.