Filefish uses 'smell camouflage' to hide from predators

By Kate Wheeling - Dec. 9, 2014, 7:15 PM

The harlequin filefish is a master of disguise. The reef-dwelling fish (Oxymonacanthus longirostris) sports a brightly colored pattern that allows it to fade into the coral it calls home. Now, scientists have discovered that the filefish doesn’t just look like a branch of coral—it smells like one, too. The researchers report online today in the Proceedings of the Royal Society B that the animal picks up the smell of the corals it feeds on, which serves as a handy disguise from the cunning predators that use odor to hunt down their prey. To identify this chemical camouflage, the team placed cod—a common predator of reef fish—in tanks with filefish and a species of coral that either matched their diet or a coral species the fish hadn’t been feeding on. The filefish were hidden inside perforated containers within the aquarium so that the cod could only smell, and not see, their prey. The researchers found that cod were much less likely to hang out around the filefish container when the species of coral present matched the reef fish’s last meals. Exactly how the filefish retains the coral smell is still unknown, but the disguise even fooled coral-feeding crabs. When the researchers gave the crabs a choice between their favorite corals and a filefish that fed on their favorite corals, they often chose the filefish. Many invertebrate species, like caterpillars, are known to incorporate compounds from the plants they eat into the outer layer of their skin to hide from hungry predators. But the filefish is the first vertebrate species found to camouflage its smell, which means that the behavior could be even more widespread across the animal kingdom than previously thought.