Abundance and feeding mode of Russian spirlin, Alburnoides rossicus, in the rhithral and potamal of Eastern European Rivers

Knowledge of the feeding ecology of fishes is fundamental for understanding the processes that function at the individual, population, and community levels and for the conservation of their populations and habitats. Spirlins are widely distributed and often abundant in fast-flowing waters throughout Europe. However, data on their diets are insufficient and inconsistent. To improve knowledge of the trophic ecology of this common fish species, we studied the diet of Russian spirlin in the rhithral and potamal of rivers located in the Volga River basin. The food niches of spirlin in the rhithral and potamal differed significantly. Fishes consumed mainly terrestrial prey falling into the water in rhithral but aquatic prey in potamal of watercourses. Among aquatic invertebrates, spirlins positively selected mobile species that foraged on the upper surface of the bottom substratum. Aufwuchs were abundant in stomachs, but, apparently, fish did not assimilate them, because intact cells occurred throughout the intestine. Spirlins in all rivers were predominantly insectivorous, not consuming or rarely consuming invertebrates that dominated zoobenthos, mollusks, oligochaetes, and leeches. This specialization, apparently, contributes to the resource partitioning with other fishes inhabiting hyporhithral and epipotamal of watercourses.