Filefish’s Camouflage: Smelling like Coral

If you eat garlic, your breath smells like it. But the orange-spotted filefish, which feeds exclusively on Acropora corals in Australia, takes that one better: Its whole body smells like the corals it eats. While your garlic breath may disclose you to your predators, the coral smell hides the filefish from its predators, such as the potato cod.

This is the first time scientists have discovered a vertebrate chemically camouflaging itself via its diet, said Rohan Brooker of the Georgia Institute of Technology, who led a study with results that appeared last month in the journal Proceedings of the Royal Society B. Visual camouflage is well known in the animal kingdom, from stick-like insects to owls that blend into trees. But many other animals interpret the world mostly by smell. "For them, chemical camouflage may be far more important to stay hidden," says Brooker.

While teaching at James Cook University in Australia, Brooker and colleagues captured filefish near Lizard Island on the Great Barrier Reef. They placed the fish in large aquariums and divided them into two groups -- one that ate an exclusive diet of the coral species Acropora spathulata and one that ate only Pocillopora damicornis, which is not part of the filefish's regular diet. The fish ate this diet for four weeks. To find out if the fish smelled like coral, the team also captured two species of small crab, Tetralia glaberrima and Trapezia cymodoce, which dwell inside Acropora and Pocillopora, respectively. These crabs were added to both fish groups. As expected, T. glaberrima crabs clearly preferred the smell of the filefish that had eaten Acropora over those fed Pocillopora -- indicating the fish were taking on Acropora's scent. The filefish's scent was so strong, in fact, some crabs treated the filefish as if they were coral.

After verifying the filefish had adopted the coral's smell, Brooker's team caught a predatory cod species and added it to the aquariums. The cod spent less time hunting around the filefish that ate Acropora than around the fish that ate Pocillopora, indicating that it could not detect the Acropora-eating filefish. The conclusion? By smelling like coral, filefish can blend in and avoid predators. So next time you see a filefish, think about the unique way it protects itself.