THEY CHEAT

If you want proof that fish have more than the fabled three-second memory, look no further than cleaner wrasse. Every day, they pick parasites and dead skin from hundreds of other fish – and they remember each individual fish and adjust their services accordingly.

Scuba-diving scientists have spent hundreds of hours watching cleaner wrasse at work on coral reefs. They’ve seen that when large predators such as groupers show up the wrasse offer an honest service. But when they’re cleaning harmless herbivores, like parrotfish, the wrasse will sometimes cheat. Instead of removing parasites, they slurp slime from the fish’s skin. Not only is slime more nutritious than parasites, but it also contains sunscreen, which stops the wrasse getting sunburnt. Even when it cheats, a wrasse apologises by massaging the other fish with its fins and persuading them not to swim off in a huff.