メジナ幼魚の社会構造 : 順位となわばり

抄録

1. Girella punctata GRAY is one of the common inhabitants at the reefy shore near the Seto Marine Biological Laboratory of the Kyoto University. The young fishes, hatched out in the early spring, attain the size of ca. 3-7 cm in summer, usually make schools(composed of 10-200 individuals), swim about here and there near the sea-beaten reefy shore, and feed on algae or small invertebrates(Table 1). 2. Although no sign of social hierarchy are recognizable in the open sea, dominance and subordination relationship appears when they are confined to the tide pool at low tide. At first they swim about freely in these pools, making groups or solitarily, but after 10 to 20 minutes the pecking behaviors appear gradually, and the social dominance order is established. In the meanwhile, No.1 individual shows a tendency to stay at a particular place. which becomes its territory. Then other fishes occupy their territories successively according to the dominance order, i.e., the higher, the faster the establishment of the territory, and consequently occupy a more favorable place for feeding or hiding. These social organizations are exhibited most distinctly at about the time of low tide ; after that they become less and less conspicuous, and disappear at last when the open sea water begins to pour into the pool(Fig. 1,Table 2), The most dominant individuals usually wander freely in the pool, whereas subordinates are attacked when they approach the territory of the dominant or of individuals of higher rank. The fishes of low social rank sometimes fail to establish territories. 3. Many similar observations performed at tide pools as well as aquariums are described(such as shown in Figs. 3,4). The fishes demand a good place where food is available and where they can be hidden from enemies, and it will be natural that the most dominant individual occupies the most favorable place. 4. In conclusion, these facts seem to indicate, so far as young Girella punctata confined in the tide pool concerns, that the hierarchy organization and the territorial organization are not the antagonistic social principles, but the latter may be taken as a revelation of the former-an expression of the desire for the area which is satisfied according to the dominance order. 5. Considering with a number of works carried on some fishes, pigeons, horses, rabbits, deers, and monkeys, the writer became of the opinion that, in the animal world, there are many cases in which the above conclusion may fundamentally be applicable.