Fish need to remove parasites which live on their skin and scales and inside their mouths.

If these parasites are not cleaned away, they can multiply and cause illness.

When fish need cleaning, they head for the nearest cleaning station where special fish or shrimp nibble off dead tissue and parasites. The cleaners even swim into the mouths of the larger fish to clean their teeth of food particles.

Certainly seems like everyone wins. The cleaners get a meal, and their clients get rid of bothersome parasites.

Recent studies show the relationship is not quite that simple though. It appears some cleaners bite. Instead of just skimming off the parasites they also take a little taste of healthy flesh – a behavior referred to as cheating.

Not a total shock, but the interesting part is studies suggest reef fish pay attention and remember how the cleaners did their job – and show a preference for those cleaner fish that are less likely to bite.

A study of fish with a choice (more than one cleaning station available) found most were likely to return to the same cleaning station if the previous interaction had ended without conflict but many changed cleaning stations for their next inspection if they had been cheated, even though the overall service quality between stations appeared to be similar.