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How Do Cleaner Shrimp Know They Won't Get Eaten When in a Fish's Mouth?

A new study has answers.

Cleaner shrimp are tiny shrimp that will eat dead skin and parasites from other fish's gills and mouths. But how do they know the fish won't eat them when they do the cleaning? Researchers recently discovered that cleaner shrimp and their clients actually have a system of communicating with each other in order to form a partnership.

When researchers fed chopped-up cleaner shrimp to the same fish that often get cleaned by them, the fish happily ate it. This confirms that the shrimp are not toxic or unappealing.

The fish really are showing restraint when they allow the cleaner shrimp to climb into their mouths.

But how do the fish and the shrimp come to an understanding that they will help each other? To figure this out, researchers set up GoPro cameras in coral reefs off the Caribbean island of Curaçao, where cleaner shrimp set up shop.

Cleaner shrimp will actually form teams of three to five and plant themselves in a particular place where fish can come to receive their services.

It's almost like setting up a carwash and waiting for customers to come.

The GoPro footage showed that when a fish approached a shrimp carwash, the shrimp waved their long, white antennae.


The researchers think that this gesture means "I'm willing to clean," because 80 percent of the time the shrimp waved, they ended up cleaning the fish they waved at. When the shrimp did not wave their antennae, however, they were much less likely to clean.

How does a fish communicate that it wants a cleaning?

The GoPro footage showed the fish changing color from light to dark when they approached the carwash.


The researchers think this color change means, "I promise I'm not going to eat you. I really want a cleaning."

The experimenters tested this hypothesis in the laboratory, where they showed cleaner shrimp light or dark shapes on an iPad. The shrimp were much more likely to try to clean dark-colored shapes.

After analyzing 199 encounters between cleaner shrimp and fish, the researchers felt confident that there has to be a mutual signal in order for the partnership to work. If the shrimp don't wave, or if the fish don't change color, cleaning never occurs.

The study demonstrates an interesting case of inter-species communication that is used to successfully suspend the predator-prey relationship in favor of a mutualistic relationship.

Shrimp and fish may actually be smarter than we give them credit for.


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