A special mucous coating that serves as a chemical camouflage allows clown fish to live among the deadly tentacles of the unsuspecting sea anemone whose form, bright and varied colors, and cluster of tentacles superficially resemble a flower). Utterly dependent on this unlikely host for protection from predators, clown fish have evolved in isolated communities, a pattern that has led to unusual behavioral adaptations.
The rigidly defined hierarchy of each clown-fish community is dominated by a monogamous breeding pair consisting of the largest fish, a female, and the next largest, a male, attended by a fixed number of sexually immature fish ranging in size from large to tiny. A remarkable adaptation is that the development of these juveniles is somehow arrested until the hierarchy changes; then they grow in lockstep , maintaining their relative sizes. While the community thus economizes on limited space and food resources, life is risky for newly spawned clown fish. On hatching, the hundreds of larvae drift off into the plankton. If, within three weeks, the defenseless larval clown fish locates a suitable anemone , it may survive. However, if an anemone is fully occupied, the resident clown fish will repel any newcomer.
Though advantageous for established community members, the suspended and staggered maturation of juveniles might seem to pose a danger to the continuity of the community: there is only one successor for two breeding fish. Should one of a pair die, the remaining fish cannot swim off in search of a mate, nor is one likely to arrive. It would seem inevitable that reproduction must sometimes have to halt, pending the chance arrival and maturation of a larval fish of the appropriate sex.
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