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

Interspecific relationships between ayu Plecoglossus altivelis and pale chu b 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 fe eding behavior towards algae and other objects which were drifting in the c urrents or fell onto the water surface in areas with slow currents. Both ay u and pale chub attacked conspecifics with larger fish tending to be domina nt. Pale chub never attacked ayu, but ayu occasionally attacked pale chub t hat invaded their territory, regardless of their body size. When ayu was pr esent, pale chub employed algal feeding less frequently and snapped at an o bject on the water surface more frequently. The feeding behavior and habita t 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 ne gatively affected by the presence of one another, presumably due to the fle xible habitat use and feeding behavior of the omnivorous pale chub.