Why can clownfish live among sea anemone tentacles without being stung?

Clownfish are able to live among the tentacles of sea anemones without being harmed by the anemone's nematocysts—specialized stinging cells used to immobilize prey—primarily due to a protective mucous coating on the fish's body.12

This mucus acts as a shield that prevents the anemone from recognizing the clownfish as food, thereby inhibiting the stinging behavior that would otherwise be triggered by contact. While it is not fully understood whether the fish produces this mucus itself or acquires it through initial contact with the anemone's tentacles, the coating is essential for the fish's survival; without it, the clownfish would be vulnerable to being stung and consumed. Additionally, there is evidence suggesting that clownfish may possess some level of physiological resistance to the anemone's toxins.12

This mutualism benefits both parties: the anemone provides the clownfish with a safe refuge from predators, while the clownfish cleans parasites from the anemone and drives away other fish that might feed on the anemone's tentacles.12