Why do anemonefishes inhabit only some host actinians?

Entacmaea quadricolor the most abundant and widespread host actinian at Lizard Island and throughout the range of the association, is also arguably the most attractive to anemonefishes. The author believes its vulnerability to predation was a factor in its evolving whatever makes it desirable to fishes. Experimental transfers pitted fish of one species against those of another, controlling for ecophenotype of host, and sex, size and number of fish. Competitive superiority was in the same order as abundance and over-all host specificity: Premnas biaculeatus, Amphiprion melanopus, A. akindynos . At least three factors are necessary to explain patterns of species specificity -- innate or learned host preference, competition, and stochastic processes.