Clownfish and sea anemones have a mutualistic symbiotic relationship, each providing a number of benefits to each other. The different actinic species generally harbor specific fish, in particular the sea anemones of the genera Heteractis and Stichodactyla, and the species Entacmaea quadricolor is a frequent clown partner. The sea anemone protects the clownfish from predators, and provides food through the remains left by the anemone meals and the occasional dead tentacles of the anemone. In return, the clownfish defends the anemone of its predators and parasites. The anemone also takes nutrients from clownfish excrement (and its other occupants: other small fish, crabs, shrimps ...), and it functions as a safe nesting site. Nitrogen excreted by clowns increases the amount of symbiotic algae (zooxanthellae) incorporated into the tissue of their hosts, facilitating the growth and regeneration of the anemone. It has been theorized that clownfish use its bright color to attract small fish in the anemone, and that clown activity creates greater circulation of water around the sea anemone (promoting some exchange ionic). Clown studies have found that clownfish modify the circulation of water around the tentacles of sea anemones by certain behaviors and movements such as "wedging" and "switching". The aeration of the tentacles of the host anemone provides benefits to the metabolism of both partners, mainly by increasing the body size of the anemone and for both, clownfish and anemone, respiration (oxygenation).
Clownfish, cardinals, Apogon, some damselflies and a few small species of goby are among the few species of fish that can avoid the powerful poison of a sea anemone. There are several theories about how they can survive the poison of anemone cnidocysts:
The mucus layer of fish may be based on sugars rather than proteins. This would mean that the anemones fail to recognize the fish as a potential food source and do not release their nematocysts with their pungent and poisonous organelles.
The coevolution of some clownfish species with specific species of host anemones may have led to the acquisition of immunity to nematocysts and the toxins of their host anemone. Experimentation has shown that Amphiprion percula can develop resistance to the toxin of Heteractis magnifica, but it is not fully protected because it has been shown experimentally to be able to die when its skin, free from mucus, has been exposed to nematocysts. from his host.