Feeding habits of the African big barb, Labeobarbus intermedius (Rüppell, 1836) (Pisce: Cyprinidae) in Beles River, Ethiopia

Labeobarbus intermedius is a key fisheries species in Ethiopia, yet its feeding ecology in the Beles River, a critical tributary of the Blue Nile feeding the Grand Ethiopian Renaissance Dam (GERD), remains understudied. This study quantified the diet composition of L. intermedius using frequency of occurrence and volumetric analyses of gut contents from 457 specimens (total length: 11.6–49.3 cm; total weight: 18–1,491 g) sampled from fishers’ catch between January and September 2023 at Digadam landing site. Detritus (42.1%) and phytoplankton (41.5%) dominated the diet, followed by macrophytes (7.2%), insects (4.3%), zooplankton (3.4%), and gastropods (1.5%). Pronounced ontogenetic dietary shifts occurred: smaller fish (< 25 cm TL) primarily consumed insects (28.5%), gastropods (26.8%), and zooplankton (19.9%), while larger individuals (> 35 cm TL) transitioned to macrophytes (30.1%), phytoplankton (23.5%), and detritus (23.1%). No significant seasonal dietary variation was detected. The dominance of low nutritional value detritus suggests reduced availability of high-quality prey, indicating potential ecological stress. These findings highlight trophic plasticity in L. intermedius and provide essential data for conservation in the Beles River ecosystem.