Clever Filefish Play Hide-and-Seek in Smelly Corals

The clever filefish apparently likes to play hide-and-seek from predators in smelly corals, a new study says, by using a type of chemical camouflage to disguise its smell. This gives a whole new meaning to the old adage, "you are what you eat."

"For many animals, vision is less important than their sense of smell," study lead author Dr. Rohan Brooker, from James Cook University, said in a statement. "Because predators often rely on odors to find their prey, even visually camouflaged animals may stick out like a sore thumb if they smell strongly of 'food.'"

So while spotted cheetahs in forests, stick-like insects among branches, and dark-colored moths on tree bark may blend into the background, Orange-spotted filefish (Oxymonacanthus longirostris) are thinking one step ahead.

These coral-eating fish feed exclusively on Acropora corals in Australia, ingesting the chemicals they contain and subsequently masking their own smell with that of their food.

In order to determine if this method was clever enough to fool filefish predators, Brooker and his colleagues captured filefish from the Great Barrier Reef and placed them in large aquariums. For four weeks, one group ate their typical Acropora spathulata coral diet, while another ate another type of coral, Pocillopora damicornis.

When predatory cod were thrown into the mix, they reportedly spent less time hunting around the filefish that ate Acropora than around the fish that ate Pocillopora.

"A finely-tuned combination of visual and chemical camouflage may be an effective anti-predator strategy that helps the fish to avoid being eaten," added co-author Doug Chivers.

And not only did the filefish confuse its predators, but crabs were also bamboozled, unable to distinguish fish from coral. Of course, the trick does not work if they eat one kind of coral and then hide in another one with a different smell.

This is not the first time researchers have seen an animal hiding itself in its food, either. The Biston robustum caterpillar, for example, takes on the smell of the plants it eats via molecules that enable it to evade predatory ants. This is just the first time the technique has been seen in higher order animals, such as fish.

But filefish may soon run into trouble, as corals like those in the Great Barrier Reef are rapidly disintegrating as a result of ocean acidification. Soon, they may have nowhere to hide.

The findings were published in the journal Proceedings of the Royal Society B.

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