Ocellaris Clownfish

Male first, female later

Every ocellaris clownfish matures as a male, and any of them can later turn female. Biologists call that being a protandrous hermaphrodite. One host anemone typically holds a breeding pair plus up to four juveniles that do not breed. The bigger fish of the pair is the female. She stops her mate from turning female, and he stops the juveniles from maturing into males.

Lose the female and the group reshuffles. Her mate changes sex and rapidly grows, and the next largest male usually becomes the new breeding male.

Dad does the nest work Once the eggs are laid, the male tends the nest for six to seven days, rarely helped by the female. He fans the eggs with his pectoral fins to aerate them and sweep off settled debris, eats any that are infertile or damaged, and aggressively chases off predators.

How big, how old

The average length is 8 cm (3.15 in), and the species can reach 11 cm (4.3 in). A clownfish lives about 8 years in the wild, and 12 years or more in a protected environment.

Over-collecting for the aquarium trade has hit populations in some areas, but the IUCN Red List rates the species Least Concern.

A home that stings

It is native from the Andaman Sea to northwest Australia, central Indonesia, the Philippines and southwest Japan. It lives on coastal seaward reefs and in shallow, sheltered lagoons at depths of 1 to 12 m (3.3 to 39.3 ft), and it depends on three host anemones: the magnificent anemone, the leathery anemone and the giant carpet anemone. It rarely strays more than 30 cm (12 in) from its host.

An anemone’s stinging cells are called nematocysts, so why do they spare the clownfish? Some researchers believe the fish’s mucus coat has a special biochemical makeup, so the anemone fails to recognize it as food and does not fire. Others theorize the mucus carries the same chemical signature as the host itself.

What is known is that a clownfish away from its host for a while has to re-adapt to the stings. On its return it performs a dance-like ritual, touching the tentacles first with only its ventral fins, then its whole belly. Acclimation takes several hours.

Its diet is mostly zooplankton (tiny drifting animals), with bottom-dwelling invertebrates and algae on the side.