Clownfish weave effortlessly through the venomous tentacles of their sea anemone hosts using a “Trojan horse” strategy that prevents the anemone from recognizing them as prey.

Sea anemones use nematocysts, tiny, harpoon-like structures filled with toxins, to capture prey. These cells fire when they detect certain chemical signals, including sialic acid, a sugar found on the surface of most marine animals.

When a fish brushes against an anemone, its sialic acid triggers the anemone’s defensive response, leading to a venomous sting.

Research published in BMC Biology found that anemonefish have dramatically lower levels of sialic acid in their mucus. Sialic acids have important biological functions and clownfish regulate the production in their mucus only to allow them to live symbiotically with the anemone.

While the researchers at Okinawa Institute of Science and Technology still don’t know how the anemonefish do this, their study found juveniles initially have high sialic acid levels and are vulnerable to stings, but as they grow, their mucus composition changes, offering some insight to potential mechanisms.

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