16-7-2024 ROTTERDAM ZOO, NETHERLANDS - ANEMONE FISH (Genus Amphiprion)

Amphiprion is a genus of ray-finned fish which comprises all but one of the species of clownfish or anemonefish in the subfamily Amphiprioninae of the family Pomacentridae.

Fish of the genus Amphiprion  are commonly called "clownfish". They belong to the family Pomacentridae, which also includes damselfishes. In many ways, they resemble cichlids and serranids.

The clownfish first came to the world's attention in 1881 when the first specimens were shown to the public in a seawater aquarium. Symbiosis with the anemone, present in all species, has been known since the mid-twentieth century. The development of diving and underwater science has led to numerous discoveries, and it is hoped that new species will be described in the future.

The films Finding Nemo and Finding Dory have made these species famous. Both have sparked a great deal of enthusiasm in the aquarium world. Initially, these species were not bred in captivity, and many populations have suffered from overfishing in the 2000s. Some populations have even disappeared locally, such as at Cape Rachado in Malaysia. Conservation measures and the development of captive breeding have helped to improve this situation.

In 2020, the genus Amphiprion  comprises 29 species that are morphologically distinguished by the number of bands (from 0 to 3) and by their colour (orange, yellow, red, black). They are all found in the shallow tropical waters of the Indian and Pacific Oceans. They are characterised by their bright colours and a particular lifestyle, closely linked to their hosts, the anemones.

Clownfish are territorial and rarely stray far from the anemone in which they live. Of the 1,000 species of anemones, only about ten are hosts for clownfish. The geographical distribution of these fish is entirely linked to that of these 10 anemones.

In the richest coral areas, up to five species of fish can be found in the same number of anemones. These anemones are only present at shallow depths, as they are closely linked to a microscopic algae that needs sunlight to carry out photosynthesis. They are therefore limited to around fifty metres and their number decreases with the depth and turbidity of the water.

Although they generally live on coral reefs, clownfish can actually live anywhere where anemones are present. Like jellyfish and corals, anemones can cause burns via their stinging nematocysts. They possess poisonous tentacles. The function of the relationship between clownfish and anemone is not yet fully understood.

The most likely hypothesis is that it is due to the protection provided by the mucus.  After a display in which the clownfish avoids being stung, it covers itself with the anemone's mucus, which gives it chemical camouflage. The constant coming and going of the fish to its host could validate this theory. A second theory suggests that the presence of anemone mucus in the fish is the result of protection and not the cause of it. According to this theory, the clownfish's mucus has evolved to be chemically compatible with the anemone.