Bagrus bayad is a freshwater fish with high commercial value in northern Nigeria. This study was conducted to assess the stomach contents and changes in diet composition of Bagrus bayad from Zobe reservoir with increasing fish size. 126 specimens of B. bayad were obtained from the artisanal fishermen’s catches at the reservoir from May to December 2021. About 85.50% of the sample had food in their stomachs, while 14.5% were empty. The stomach contents analysis reveals the presence of fish species: Tilapia zilli, Alestes baremose, Petrocephallus bane, Clarias gariepinus, fish eggs, molluscs, aquatic insects, and detritus as food components. The food with the highest percentage frequency (%f) of occurrence in the young Bagrus (≤ 30 cm TL) was insects (26%), while crustaceans (28%) and teleost fishes (46%) recorded the highest % of in juvenile Bagrus (30.0-60.0 cm TL) and adult Bagrus (≥ 60.0 cm TL), respectively. Invertebrate groups dominated the gut content of young and juvenile Bagrus, with a cumulative percentage numerical abundance of 50.7% and 57.8%, respectively. Debris was found only in the stomachs of young Bagrus, accounting for a percentage numerical abundance of 31%. The percentage index of relative importance was highest (42.57%) for debris in young Bagris, while in both juvenile and adult Bagrus bayad in Zobe reservoir, teleost had the highest IRI of about 77%. This study showed that the species is piscivorous. The young are detritivores, while the juveniles also prey on insects.