Clownfish spend their entire lives with their host anemone, rarely straying more than a few yards from it. They lay their eggs about twice a month on the nearest hard surface concealed by the fleshy base of the anemone, and they aggressively protect the developing embryos. Just after a clownfish hatches, it drifts near the surface for a week or two as a tiny, transparent larva. Then it metamorphoses into a miniature clownfish less than half an inch long that descends to the reef. If the young fish doesn’t find an anemone and acclimatize to its new life within a day or two, it will die.
Among scientists, clownfish are also known as anemonefish because they can’t survive without a host anemone, whose stinging tentacles protect them and their developing eggs from intruders. Of the roughly thousand species of anemones, only ten host clownfish. It’s still a mystery exactly how a clownfish avoids being stung by the anenome, but a layer of mucus—possibly developed by the clownfish after it first touches an anemone’s tentacles—may afford protection. The clownfish, in effect, becomes an extension of the anemone and another layer of defence against anemone-eating fish. What’s good for the clownfish is good for the anemone, and vice versa.
A dozen or more clownfish of the same species can occupy a single anenome. Cruising around their anemone, they snag plankton, algae, and tiny creatures such as copepods, often hiding within the folds of their host to eat the larger food items.
Clownfish may or may not become sexually mature adults. A strict hierarchy exists among the occupants of each anemone, which hosts only one dominant pair at any time. The female is the largest in this “family,” followed by the male and the adolescents. A mature pair assure their continued dominance by chasing the juveniles, causing them stress and reducing their energy for food foraging.