Scumbag Fish Changes Color to Trick Baby Fish so It Can Eat Them

​Animals using mimicry to trick prey or avoid predators is a common phenomenon in nature. But researchers at Cambridge recently discovered that a little, color-changing coral fish is particularly badass when it comes to playing dress-up.

The dusky dottyback is a cute, harmless-looking little fish. It's about three inches long, lives in Indo-Pacific coral reefs, and ranges in color from pink to grey. And according to ​a paper published today in Current Biology, this pretty little swimmer changes its color to trick baby fish of other species into thinking it's one of them. Then the dusky dottyback eats them.

It's been known for a while that dottyback fish can change color depending on its environment, but researchers didn't know much about why or how it morphed from one color to another.

To find out, the team at Cambridge looked at yellow and brown-colored dottybacks in particular. They placed the fish in one of two different environments (bright green and yellow live reef, or darker brown dead coral rubble) with one of two different colored groups of damselfish (a favorite prey of the dottyback): brown or yellow.

They found that even if it meant no longer matching its5 coral surroundings, the dottyback would always change color to match that of its prey. It could then use its new deceptive coloring to get close to the juvenile damselfish and chow down, according the paper.

"Dottybacks were significantly more successful at capturing juvenile damselfish when their color matched that of adult damselfish," the paper reads. "This is probably due to the prey exhibiting reduced anti-predator vigilance when unable to detect differences between harmless models (adult damselfishes) and predatory mimics (dottybacks)."

They also investigated how the dottyback changes color. Unlike other color-swapping fish, researchers found that the number of chromatophores—the cells that contain pigment, kind of like the fish version of our melanocytes—in the dottyfish stayed the same. What changed was the ratio of yellow pigment cells to black pigment cells, which combine to give the fish a different hue.

This unique talent provides the dottyback several advantages, according to the paper. Not only does it allow the dottyback to more easily approach juvenile damselfish without detection, but it also makes it hard for the damselfish to adapt to the dottyback's tricks. The dottyback can move to new groups of fish and easily switch to whatever color it needs (within the natural color range of dottybacks) to in order to dupe the new, unsuspecting group.

"This is comparable to a 'wolf in a sheep's clothing' scenario," the paper continues. "Distinguishing the predator from harmless [members of the same species] becomes increasingly difficult when they look alike, regardless of whether or not the model species matches the appearance of the prey."

The dottyback's talent also enable it to camouflage with its environment (damselfish typically chill in coral that is close to their coloring), making it harder for predators to detect them.

And while the dottyfish is far from the only animal able to change color or mimic other species, its ability to easily transition from one color to another for the express purpose of fooling its prey is unique.

"This is the first time that an animal has been found to be able to morph between different guises in order to deceive different species," William Feeney, a zoology researcher at Cambridge and co-author of the study, said in a release. "The dottyback [is] a pretty crafty little fish."