Critter of the Month - Cleaner wrasse

Joshua - My name is Joshua Drew, I am a research biologist here at the Field Museum of Natural History in Chicago, Illinois and my favorite marine creature is the cleaner wrasse, Labroides dimidiatus...

This fish is just amazing. Every time I go underwater and I see it I am mesmerized by it. It does so many interesting things.

The thing I find most interesting about the cleaner wrasse is that, like the name suggests, they perform a cleaning service and what will happen is that these fish will sit out pretty obviously on the reef and they advertise their presence by bobbing up and down. And what will happen next is that other fish that have a lot of parasites will come up to these cleaning stations and sit there and hover with their mouths open and the cleaner wrasse will pick all over the fish taking off ectoparasites like little isopods or in some cases even leeches and it will clean up all the different groupers and wrasses that come through.

And this is not only a really important ecological service because it has been shown that when you remove cleaner wrasses the species diversity on reefs goes down. But as you can imagine it actually performs a very valuable health service for the fish, being cleaned.

And we have had other different studies shown that when you remove cleaner wrasses the parasite load, perhaps not surprisingly, on those fish shoots up and their overall health diminishes. So the cleaner wrasse is a really interesting fish for me because it provides such useful service, that even though it's in and of itself is a bite size meal, it can enter into the mouths of predatory fishes like groupers and snappers with impunity because its more worthwhile for those groupers and snappers to have those parasites removed than it is to grab a little snack.

Now the other thing that is really cool about this is that there are two other species of fish that actually mimic the cleaner wrasse, so they look just like the cleaner wrasse but they have these really long, nasty fangs and they'll swim just the same way that the cleaner wrasse does and when an unsuspecting grouper or snapper or parrot fish comes up to the mimic and presents itself to get cleaned instead of having say the isopods removed from it, or the parasites removed from it, these mimics will come up and take a little bite out of the fish and then dart off into a whole before the fish, who was hoping to get a cleaning and instead got a little nip taken out of him, can retaliate.

Now I think that is just a really interesting example of mimicry and evolution on coral reef fishes, and the cleaner wrasse is just one of those characteristic members of Indo-Pacific reef fauna and they are just an amazing little guy to watch.