Mimic octopuses (Thaumoctopus mimicus) have one-upped their well-camouflaged cousins by actively impersonating other sea creatures—such as venomous sea snakes and lionfish—by changing their body shape and movement. But they have now been one-upped by a tiny fish that mimics them (or at least takes advantage of their complex patterning and movement to better camouflage itself).

A black-marble jawfish (Stalix histrio) was spotted last July in Indonesia swimming among the arms of a mimic octopus. The encounter, which was filmed by Godehard Kopp of the University of Gottingen, was described as "opportunistic mimicry" last month in a paper in Coral Reefs.

"There are some cases in which many species mimic the same model," Luiz Rocha, of the California Academy of Sciences, explained to me via email. But as far as a mimic-inspired camouflage behavior, "this is a first," he says.

Why do the researchers think the fish is mimicking the octopus—and not the original model, such as a lionfish or sea snake? "The jawfish matches the color of the mimic octopus, but it only gains protection when it swims beside the octopus," Rocha says. "So, if the jawfish was just sitting over open sand it probably wouldn't look like a lionfish." The shy little jawfish, which spends most of its time hiding in burrows in the sand, seems to be taking advantage of the advanced disguises of the bigger, bolder octopus, darting around its stripped arms—a strategy that could easily mask it to visual predators.

Plenty of organisms have disguised themselves to look like other, less appetizing objects (take a walking stick insect or a viceroy butterfly). And other fish have been observed engaging in such opportunistic mimicry (such as the bluestriped fangblenny, which masquerades as a cleaner wrasse when they inhabit the same waters). But researchers have puzzled over how complex behavioral mimicry adaptations might have evolved. This newly described mimic-mimic might offer some clues. "My best guess is that the color came first, and the behavior of following the octopus came later," Rocha says. "After many generations the ones that resembled more the octopus pattern probably had a better chance of survival and of leaving more offspring."

Rocha and his colleagues still aren't sure how often these copycat fishes follow the octopuses—whether they're a frequent tagalong or just an occasional accessory. "Mimicry is a fascinating subject and there is not much known about it in the oceans," Rocha says. And, he says, "we plan to study this—and other cases—in much more detail."

Video courtesy of Godehard Kopp

Illustration courtesy of Ivan Phillipsen