Abstract
Group effects on oxygen consumption of the ayu, Plecoglossus altivelis, in relation to growth stage were investigated by a polarographic oxygen electrode, using continuous flow respirometry. The oxygen consumption of an isolated fish in the respirometer tube, which either had shown signs of aggressive behavior in the aquarium when kept together with a number of fish, or had grown to 9 cm in standard length in the aquarium when kept solitarily, increased markedly when the fish was placed in visual contact with conspecific fish. However, when an isolated fish, which had neither shown signs of aggressive behavior nor grown to 9 cm in standard length, was placed in the same visual condition, its oxygen consumption decreased or did not change. Such an excitatory group effect on oxygen consumption seems to be established depending on the habit of solitary living and aggressive behavior, while a soothing group effect seems to be caused by the habit of schooling, according to growth stage.
