Photograph courtesy Godehard Kopp

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A small jawfish (see red arrow) mimics a mimic octopus in a video still from a new study.

Photograph courtesy Godehard Kopp

Fish Mimics Mimic Octopus That Mimics Fish

"We've never seen anything like that before," scientist says.

The mimic octopus can take on the forms of a lionfish, a jellyfish, a shrimp, a crab, and more than ten other animals. But now a jawfish in Indonesia has been filmed one-upping the marine master of disguise—it mimics the mimic octopus.

Researcher Godehard Kopp was diving off South Sulawesi Province (map) when he noticed a tiny yellow-and-black striped fish swimming alongside a similarly colored mimic octopus.

Surprised, Kopp, of the University of Göttingen in Germany, filmed the event and sent the video to biologists Luiz Rocha and Rich Ross at the California Academy of Sciences and for their interpretation.

Rocha and Ross only compounded the mystery. "We've never seen anything like that before," Rocha said.

Jawfish Makes Like a Ninth Arm

Jawfish normally stay hidden in ocean burrows, avoiding predators. "I've never seen one swimming in the open," Rocha said.

But the jawfish in the video, wiggling its body "almost like a tentacle," closely follows the mimic octopus for at least a quarter of an hour—filming was cut short after 15 minutes, when Kopp had to come up for air.

The fish probably stuck close to the octopus—which didn't seem to notice its "hitchhiker"—to take advantage of the camouflage while looking for food or a new burrow. But the researchers don't yet know which.

They're also not sure whether the event is a one-off or whether the jawfish "does that every time" an octopus comes by, Rocha said.

(Also see pictures and watch video of octopuses that carry coconuts as instant shelters.)

Octopus-Mimicking Fish a New Species?

Adding to the odd situation, the jawfish's species is even in question.

It looks like a black-marble jawfish, aka harlequin jawfish, aka Japanese jawfish—a variety thought to have a range stretching from southern Japan south to Indonesia, the home of the mimic octopus.

But because this is the first time a jawfish has been documented performing any kind of mimicry, Rocha said, he has to wonder if there's some chance the Indonesian fish might be genetically distinct from its far-flung cousins.

"We're not even sure if the jawfish [throughout that range are] actually one species," Rocha said. "The one from Indonesia might even be a new species."

The octopus-mimicking fish study appears in the current edition of the journal Coral Reefs.