currentsinbiology:

Scamming Nemo: How cleaning fish are the ‘con-men’ of the coral reef

Cleaner wrasse perform a cleaning service for coral reef fish –
namely eating parasites off their customer’s skin. However, what the
females of some species actually want is to lure in clients and ‘cheat’
them by biting off some tasty mucus before escaping.  

This elaborate scam works much like how we would encounter in human
societies. “When they are producing eggs, female cleaner wrasse desire
mucus for particular nutrients that they wouldn’t normally get from
parasites, whereas males rarely cheat,” explains researcher Dr Sandra
Binning at the University of Neuchâtel, Switzerland. “Their clients
don’t want to lose this mucus, so the cleaners use ’tactical deception’
– that is, attract them with the promise of an ‘honest’ parasite
cleaning service.”

Cleaners prefer to cheat bigger fish over smaller fish, because they
can pick off more mucus from the large fish. In fact, they even provide
honest services to smaller fish while the large fish watch, hoping to
tactically entice them in. “There are limits though,” adds Dr Binning.
“Very big predator fish are never cheated because they can severely
punish the cleaners for bad behaviour.”