Clownfishes, or nemos as they are called, are fishes in the family Pomacentridae. 29 species are recognized in this family. In the wild they all form symbiotic mutualisms with sea anemones. Depending on species, clownfish are overall yellow, orange, reddish, pink or blackish, and many show white bars or patches. The largest adults can reach a length of about 18 centimeters, while some can be as small as 10 centimeters.

2 clownfishes in a heteractis anemone.

Clownfish are native to warmer waters of the Indian and Pacific oceans, including the Great Barrier Reef and the Red Sea. While most species have restricted distributions, others are widespread. They are generally highly host specific, and especially the genera and the tip anemone (quadricolor), are frequent partners.

A Clark's anemonefish in a bubble-tip anemone.

The clownfish feeds on small invertebrates which otherwise potentially could harm the sea anemone, and the fecal from the clownfish provides nutrients to the sea anemone. Clownfish are eating both algae and small fishes while the algae accounts for around 20 to 25 percent of its diet. It has also been suggested that the activity of the clownfish results in greater water circulation around the sea anemone. In addition to providing food for the clownfish, the sea anemone also provides safety due to its poison.

A beautiful shot of a family of Western clownfishes in an anemone.

Clownfishes and certain damselfishes are the only species of fishes that can avoid the potent poison of a sea anemone. There are several theories about how this is accomplished but the most common one is:

The mucus coating of the fish may be based on sugars and this would mean that anemones fail to recognize the fish as a potential food source and do not fire their sting organelles.

A Pink anemonefish hiding in her anemone.

The spawning season of the clownfish, a time when they breed, is year round in tropical waters. Males attract the females by courting. Courting behaviors include chasing, biting and extending fins. Clownfish lay their eggs in batches on coral, rock or next to the sea anemone that they call home. The male clownfish will build a nest on the rock or coral near the anemone in order to provide protection from predators. Breeding starts with the male chasing the female to the nest where the eggs are released. Depending on the species, one hundred to one thousand eggs are laid. The male clownfish guards and protects the eggs until they hatch. They hatch within 4 to 10 days.

A Bridled clownfish watching out for her anemone.

In a group of clownfish, there is a strict hierarchy of dominance. The largest and most aggressive female is found at the top. Only two clownfish, a male and a female, in a group reproduce through external fertilization. The clownfish are hermaphrodites, meaning that they develop into males first, and when they mature, they become females. Also, as mentioned earlier, more than one clownfish is able to live in a sea anemone. If the female clownfish is removed from the group, such as by death, one of the largest and most dominant males would become a female. The rest of the remaining males will move up a rank on the hierarchy