Negative effect of ayu on the growth of omnivorous pale chub inexperimental pools

摘要

The growth rate of pale chub Zacco platypus was negatively correlated with the number and biomass of ayu Plecoglossus altivelis in experiment pools regardless of their body weight. Both species were omnivorous, feeding upon both benthic algae and invertebrates; ayu fed principally upon algae whereas pale chub consumed invertebrates. Pale chub shifted their moving tactics from bottom moving to surface moving or sit-and-wait when they coexisted with; numerous ayu, presumably due to occasional attack by ayu. It seems likely that the reduced pale chub growth rate was due to interspecific aggression and exploitation of benthic algae and invertebrates by ayu.