BRIEF: Slimy ‘Kiss’ Lets Reef Fish Feed on Stinging Corals

(Inside Science) -- With their sharp, stony skeletons and stinger-laden flesh, corals are well protected against most potential predators. Tubelip wrasses are one of the few fish to overcome these defenses, and now, scientists have discovered how they do it. The secret is in the lips.

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This scanning electron micrograph image shows the mucus-oozing folds on a tubelip wrasse’s lips.

Media credits

Victor Huertas and David Bellwood

Unlike their thin-lipped relatives, tubelip wrasses have big, fleshy lips that protrude in front of their teeth. These lips appear smooth to the naked eye. But in a study published today in Current Biology , scientists examined them for the first time under an electron microscope, and saw they are actually covered in parallel flaps like the gills of a mushroom. The lips produce huge amounts of mucus, and can close to form a sort of straw.

High-speed videos revealed what the strange lips are for.

"[T]ubelip wrasses feed using short sharp ‘kisses’ to suck mucus and occasionally tissue off the coral surface,” the authors write. The kisses make a smacking sound the researchers describe as “tuk.”

According to the researchers, the lip mucus probably serves a double purpose, forming a seal on the coral’s surface while shielding the fish from stinging barbs known as nematocysts. Thus protected, the fish are free to suck out coral’s nutritious goo.

Slow-mo footage shows a tubelip wrasse “kissing” coral. Raw video courtesy of Victor Huertas. Editing by Karin Heineman.