メダカの社会生態学的研究 : I.社会行動について

抄録

1. Social behaviors of the killi-fish, with special reference to the territoriality and social hierarchy, were observed in 6 aquaria each having a diameter of 18cm. In each of the aquaria 1,2,3,5,7 and 10 pairs of the fish were released respectively. 2. Fighting occurs between the members of the groups in the aquaria almost throughout the year, even in the winter when the breeding season is over. The fighting behavior is represented in general by a sudden aggression after the approach of an individual towards the other, and a quick retreat of the latter, no mutual aggression taking place. Fighting is observed in both males and females, or even in the sexually immature fishes. 3. The patterns of social behavior differ with the difference of group densities. In the groups of 1 and 2 pairs no territory-holding individual is observed, while in each of the groups of 5,7 and 10 pairs one individual occupies a territory and the others struggle in the remaining space. In the group of 3 pairs such differentiation is obscure, though sometimes a territory-holding individual appears. The fluctuations of fighting frequencies from day to day also differ with the difference of densities, corresponding with the types of social differentiation. 4. A territory is usually established at the bottom of the aquarium, but two or more territories are seen when the space is divided into small parts by weeds. When only one territory is formed, the occupant of the territory is seemingly the most dominant individual in the group and the remaining fishes which have no territory, are subordinate ones. Therefore, it may be said that the formation of the territory is not only affected by the place factor, but also closely related to the dominance hierarchy in the group.