Feeding habits and concentrations of trace metals in different organs of the Nile catfish Synodontis schall (Bloch & Schneider) (Pisces: Mochokidae) in Lake Abaya, Ethiopia

Abstract

This study investigated the feeding habits and trace metal concentrations in different organs of the Nile catfish, Synodontis schall, in Lake Abaya, Ethiopia. Stomach content analysis was conducted using frequency of occurrence and volumetric analysis. The results of the study indicated that S. schalli is an omnivore with polyphagous feeding habits; dominant food categories included phytoplankton, detritus, insects, zooplankton, and macrophytes. Seasonal shifts were observed: phytoplankton was the primary food source during the dry season, whereas zooplankton predominated during the wet season. Ontogenetic dietary shifts were also noted with juveniles consuming mainly phytoplankton and zooplankton, while adults mainly fed insects, detritus and phytoplankton. Trace metal analysis identified copper (Cu), cadmium (Cd), nickel (Ni), zinc (Zn), and manganese (Mn) in liver, kidney and muscle tissues, while lead (Pb) and cobalt (Co) were not detected. Metal concentrations in the liver were ranked as Cu >Zn > Mn > Ni > Cd, while in muscle and kidney tissues, the order was Zn > Cu > Mn > Ni > Cd. Significant differences (p < 0.05) in mean concentrations of Cu, Cd, and Zn were noted among tissues. All detected heavy metals were within the FAO and EU safety limits, suggesting that S. schallfrom Lake Abaya is safe for human consumption.