Diet overlap of two sympatric cyprinids, Sarmarutilus rubilio (Bonaparte, 1837) and Scardinius erythrophthalmus (Linnaeus, 1758) outside their native range

This study represents the first examination of the feeding ecology of Sarmarutilus rubilio and Scardinius erythrophthalmus in the Sidi Salem reservoir, outside their native range, as well as the first investigation of the trophic overlap between these two species. A total of 951 stomach contents were analysed, with prey items identified and counted. The Prominence Values (PV) for each prey type and the diet overlap (α) between the species were estimated. Both species shared similar food resources, with macrophytes constituting the primary component of their diets, particularly for S. erythrophthalmus (%PV = 76.6). Arthropods were the second most important prey category for both species. Additionally, other prey categories, such as cyanobacteria, microalgae, and nematodes, were consumed in low proportions (%PV < 1.5). Diet variations were observed among stations for S. rubilio and among seasons for S. erythrophthalmus. The diets of the two species showed significant overlap (α > 0.6). Both species were found to have narrow niche breadths, indicating specialized feeding habits. Sarmarutilus rubilio shows feeding plasticity, while S. erythrophthalmus is predominantly herbivorous. This information is valuable for developing future fishery management plans and strategies for fish biodiversity preservation in Tunisian freshwater systems, especially since S. rubilio is categorized as a near-threatened species.