If someone at ⁞your workplace offends a client or a customer, they’d probably get an earful from their colleagues or boss. If someone annoys a friend of yours, you’d probably have a go at them. This capacity to punish those who behave badly, even if they haven’t wronged us personally, pervades all aspects of human society. And we’re not the only ones – fish punish bad behaviour too.

The bluestreak cleaner wrasse (Labroides dimidiatus) operates an underwater health spa for larger fish. It advertises its services with bright colours and distinctive dances. When customers arrive, the cleaner eats parasites and dead tissue lurking in any hard-to-reach places. Males and females will sometimes operate a joint business, working together to clean