Seasonal and ontogenetic diet shift of two sympatric cyprinid fish species from the temperate Karamenderes River, Canakkale, Turkey

Diet composition and feeding relationships of two cyprinid species, Squalius cii and Barbus oligolepis, from the Karamenderes River, northwestern Turkey, were assessed over a 1-year period. Both species were omnivorous and fed mostly on benthic plant materials (particularly algae) and insects. The diet of B. oligolepis primarily comprised Bacillariophyceae, Diptera larvae, and other insects, while that of S. cii comprised filamentous algae (Cyanobacteria and Chlorophyceae), insect larvae, and adults. Ontogenetic shifts in diet were identified in both species. The ratio of Chlorophyceae in the diet of B. oligolepis showed a gradual increase with increase in its body size; moreover, the number of ingested taxa decreased but diet diversity increased with increasing fish size. There were seasonal variations in feeding intensities of both fish, which decreased in the colder months. Seasonal resource availability was higher for S. cii than B. oligolepis; moreover, diet overlap was significant in the spring and summer. Findings indicate that S. cii may exclude B. oligolepis during limited resource availability conditions. The cooccurrence of these species may be explained by their generalist feeding strategies; ontogenetic and seasonal resource partitioning played an important role in the coexistence of these species.