Interspecific interactions between ayu, Plecoglossus altivelis, and pale chub, Zacco platypus, in artificial streams

Abstract

Interspecific relationships between ayu Plecoglossus altivelis and pale chub Zacco platypus were examined in experimental streams where ayu, pale chub or both species were stocked. Ayu predominantly employed algal feeding in areas with rapid currents, whereas pale chub were omnivorous, exhibiting feeding behavior towards algae and other objects which were drifting in the currents or fell onto the water surface in areas with slow currents. Both ayu and pale chub attacked conspecifics with larger fish tending to be dominant. Pale chub never attacked ayu, but ayu occasionally attacked pale chub that invaded their territory, regardless of their body size. When ayu was present, pale chub employed algal feeding less frequently and snapped at an object on the water surface more frequently. The feeding behavior and habitat use of ayu also differed between streams where pale chub were present or absent in some periods. However, ayu and pale chub growth rates were not negatively affected by the presence of one another, presumably due to the flexible habitat use and feeding behavior of the omnivorous pale chub.