Limited contribution of predation by zooplanktivorous cyprinids to 0+ fish mortality

Abstract

Summary Predation by zooplanktivorous cyprinids was hypothesized as substantially contributing to larval fish mortality. To test this assumption, potential predators were sampled by electric fishing at sites and times of high fish larvae densities in the lower Oder River, Germany, in 2002 and 2003. At ten sites with high prey fish densities, all fishes ≥1+ and 0+ pike – all considered potentially predating on fish larvae – were captured, anaesthetised, and fixed. In the laboratory, 982 guts, respectively, stomachs were dissected and checked for fish larvae and larvae remains. Predation on 0+ fish was detected in the primary piscivorous fishes Esox lucius L. and Aspius aspius (L.), and facultative piscivorous Perca fluviatilis L., whilst none of the other nine species examined consumed fish. These findings implicate that predation by planktivorous cyprinids did not explain the typically strong decline in larval fish densities in the first weeks after hatching.