Shrimps remove ectoparasites from fishes in temperate waters

We have found that two very common species of North Atlantic shallow water shrimp, Palaemon adspersus and Palaemon elegans, remove and feed on ectoparasites on plaice (Pleuronectes platessa L.). The relationship could be mutualistic, as we did not observe any attempts by the fishes to feed on the shrimps. The ectoparasites removed included monogenean worms (Gyrodactylus sp.) and sea lice (Lepeophtheirus pectoralis). An experiment showed that there were 65% more Gyrodactylus parasites on the fishes that had been apart from compared with those that had been together with shrimps for 48h. Shrimps on coral reefs are known for cleaning fishes, but that shrimps in temperate waters show parasite-cleaning behaviour is, to our knowledge, a new observation.