なわばりの密集した地域におけるアユの行動

抄録

"Ayu" (Plecoglossus altivelis TEMMINCK et SCHLEGEL) bas a behaviour to establish a territory, not for breeding, but mainly for feeding. In 1956,from the beginning to the end of June, a number of territories of "Ayu" covered the stone-bottom near Ukawa Bridge at the lower course of the River Ukawa in Kyoto Prefecture, as shown in Figs.1 and 3. The authors have observed in this area that the fish in territories hardly go out of their respective home range, that they do not extend their home ranges immediately after the departure of their adjoining individual from his territory, and that territory-having individuals A and B, given in Fig.2,seem to avoid contact between them. They have also observed that territory having fish drive out all invaders with the exception of those who are in the situations either in driving away their own invaders or in returning from such action. It may be induced from these behaviours that the number of times is remarkably small concerning mutual driving among neighbouring fish (as shown in Table 1). This fact may be note-worthy in territorial life of "Ayu", for, as observed in 1955 in the same river, the fish in territories spend so much time in driving out invaders, that they have no plentiful time to secure their food.