Yummy mummies

When you think of cleaner fish, you probably think of those dramatically coloured little fish on tropical coral reefs, dancing in and out of the jaws of moray eels and other large predators. But coral reef fish aren’t the only ones that pick up parasites.

Pacific salmon get lice. Sea lice, to be exact. And you have to think these are about as unpleasant as human lice. Obviously, since salmon are heavily exploited, biologists are going to be interested in ways to control potentially harmful parasites that could hurt the salmon.

Losos and colleagues discovered something, apparently quite by chance: sticklebacks were picking parasites off the salmon and eating them. Good for the salmon, who gets a parasite removed, and good for the stickleback, who gets a meal. The salmon don’t seem to solicit cleaning, like some coral reef fish do, but they don’t swim away from the sticklebacks, either. And as you can see from the picture, the sticklebacks used in the experiments are about the same size as the salmon.

But that’s not the cool part.

The cool part is that the stickleback were selectively picking off female sea lice. The sticklebacks are also doing something the authors called “cropping.” Because the eggs of a pregnant sea louse are not attached to the salmon, the stickleback can grab on to the eggs alone and pull them off without removing the louse. Even if the louse isn’t killed, “cropping” probably exerts a pretty strong damping effect on the overall population of the parasites.

This is the first time cleaning has been seen in the family that sticklebacks belong to, and the first time it’s been seen in the relatively cool waters of the Canadian Pacific.

Reference

Losos CJC, Reynolds JD, & Dill LM (2010). Sex-selective Predation by Threespine Sticklebacks on Sea Lice: A Novel Cleaning Behaviour Ethology : 10.1111/j.1439-0310.2010.01814.x

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