Y: I don't know what to do with this spa certificate I won. The idea of people--strangers--putting me into exfoliating baths or seaweed wraps doesn't float my boat.

D: Hmm. Most people go gaga over that kind of thing. In fact, fish do, too.

Y: Pardon me?

D: A fish called a cleaner wrasse spends its time cleaning parasites and dead scales and other tissue off the bodies of other fish. Cleaner wrasse reside and set up shop in areas known as cleaning stations. They're sort of the spas of the sea.

Y: Other fish let the cleaner wrasse clean them?

D: Boy, do they. They line up for the service the wrasse provides! And a lot of the wrasse's clientele are much bigger fish. These fish present themselves as passive and ready for cleaning by remaining still, spreading their fins and gills, and opening their mouths. The cleaning is a somewhat invasive process. The wrasse not only cleans the outside of the fishes' bodies, but cleans inside the gills and mouth too.

Y: What does the wrasse get out of it?

D: Why, a good parasite meal, that's what.

Y: Sounds like they risk becoming meals in the process though.

D: I suppose so, but their larger clients almost never harm them. In fact, the cleaning station is one of the few places where diverse fish congregate without showing aggression.

Y: Is it that important that the parasites be removed?

D: It's not yet certain whether the parasites pose any danger to the fish. It does seem at least that the presence of cleaner wrasse leads to reef fish diversity.

Y: Hmm. Well, too bad I can't give my gift certificate to the fish.

D: For sure.