Thieving Cleaner Fish Are The Con Artists Of Coral Reefs

A pair of blue-streaked cleaner wrasse cleaning the mouth of a potato cod. Simon Gingins, University of Konstanz

Coral reefs are like the city centers of the sea, full of cosmopolitan aquatic life zooming in and out of the labyrinthine landscape. Like city centers, many of the critters here actually have set occupations, symbiotic relationships that benefit both parties. One such slippery creature is the cleaner wrasse, who take time out of their busy swimming schedule to groom larger, often predatory fish, removing parasites at so-called “cleaning stations” that they then feed on.

However, as a new piece of research reveals, some of these cleaner wrasse are pulling a bit of a scam – and the females are the most deceptive of them all. As it turns out, predatory fish waiting to be cleaned often have a mucus lining their mouths that is particularly nutritious to egg-laying females.

The clients, however, prefer not to have this mucus snatched away from them, so the cleaners use a form of “tactical deception”, wherein they attract the clients over with the promise of an honest, fair cleaning service. They do this by removing the parasites of smaller client fish in front of them in order to give the impression that they are not inclined to engage in a bit of skullduggery.

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When the client fish saunter over, bathed in a false sense of security, the female cleaners snatch away their mucus as they are removing parasites, and sometimes the clients are none the wiser. Males, perhaps not driven by pregnancy-based gastronomic desires, are far less likely to cheat their clients overall, but it’s been known to happen.

“There are limits though,” study lead Sandra Binning, a postdoctoral researcher in eco-ethology at the University of Neuchâtel, said in a statement. “Very big predator fish are never cheated because they can severely punish the cleaners for bad behavior.”

There are nuances to this sneakiness. Addressing an audience at the annual meeting for the Society for Experimental Biology in Brighton on July 4, Binning notes that the blue-streaked cleaner wrasse adapts its strategy depending on the level of competition. In habitats with many cleaners, competition for clients is incredibly high, and the cleaners need to keep it on the straight and narrow (or at least appear to), less they are quickly spotted as being tricksters and shunned from fishy society.

Female cleaners also behave differently depending on the level of local competition. When they are egg-laying and thus desire mucus-based nutrients, they cheat with reckless abandon – so long as they are one of very few cleaners in town. However, if competition is high, they become much more deceptive.

So there you have it – coral reefs are full of cheats. Humans and wild animals aren’t so different after all.

Gifs in text from supplied video. Top – A bit of honest cleaning between several cleaner wrasse and a predatory coral trout. Bottom – A cleaner getting punished for stealing some mucus. Simon Gingins, University of Konstanz

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