Clowning Around

Clownfish and sea anemones have one of the most famous partnerships in biology. The anemone’s toxin-packed tentacles keep predators away while the clownfish picks at parasites preying on the animal. Now biologists at the University of Jordan and Auburn University have discovered a new facet of this relationship: When anemones and clownfish are in physical contact, they consume more oxygen overnight than the sum of what each consumes separately.

Clownfish don’t sit by idly in their host’s tentacles—they dance the night away. “It’s a wiggle dance, almost like fluffing a pillow, only these fish ‘wedge’ into tentacles,” says Nanette Chadwick of Auburn University. Chadwick and colleagues suspect that these movements circulate oxygen throughout the anemone during the night, when the concentration of the gas typically drops as photosynthesis slows down. The finding also suggests that separating clownfish from anemones—as is sometimes done to stock aquariums—may leave the anemones more vulnerable to their environments.

This story originally ran in the July-August 2013 issue as "Fins With Benefits."