Abstract
The anemonefish, Amphiprion xanthurus, was studied on the island of Miyakejima, Japan, from 1969 to 1972, with special interest in the problem of territory and aggression.General life history studies were also conducted in nature and in the aquarium.
Most populations consist of a pair of fish, but this is due to territorial restrictions imposed by the size of the sea anemone colony.A.xanthurus is not biologically monogamous.
Both male and female defend territories, but territorial behavior differs between sexes.Male territorial energies focus outward, in defense of the periphery of the territory, while female territories focus inward on the accessibility of male nesting holes.Female territories may be more than twice as large as male territories and may overlap the nesting holes of two or more males. Dominance seems to determine the location and size of female territories.Males are more aggressive than females in defense of nest holes against invaders.Reproductive success seems to be the primary reason for territoriality in both sexes.Males defend nesting sites throughout the year, probably due to restrictions on availability of nesting space dictated by the size of the sea anemone colony.Immatures and some low ranking adults do not defend territory.
Crowding in aquaria results in increased aggression and more obvious dominance patterns.Invariably, females are dominant over males in the aquarium and display a subtle dominance in natuie.
Both bottom organisms and plankton seem to be important food for adult anemonefish.During the breeding season nearly all the anemonefish in a colony may occasionally rise up above the anemones to feed on swarms of plankton.The frequency of courtship and agonistic displays at such times suggests some sort of social mixing function.Various crustaceans are a danger to the eggs at night, when nests are unguarded.
A.xanthurus is able to tolerate temperatures of 13°C or less, and goes into semi-hibernation in winter.Life expectancy is probably three to four years.
On Miyake, Cymbactis actinostoloides and rarely Stoichactis kenti are apparently the only sea anemones with which A.xanthurus has a symbiotic relationship.At night anemonefish hide deep within the rocks at the base of the anemone or rest in the tentacles of the anemone.
