Parasite-cleaning shrimps are not confined to the tropics as previously believed - two species live in UK waters.
Scientists have found that two coldwater shrimps, Palaemon adspersus and Palaemon elegans remove and feed on parasites on the Plaice, Pleuronectes platessa.
Cleaner shrimps are well-known in the tropics but this is the first time that parasite-cleaning behaviour has been seen in temperate shrimps.
Sara Ostlund-Nilsson and Goran Nilsson of the University of Oslo Physiology Programme in Norway, and Justine Becker of the University of Queensland said that the shrimps eat ectoparasites on the skin of the Plaice, and that the fish made no effort to eat the shrimps.
"The relationship could be mutualistic", the authors wrote in their paper in The Royal Society journal Biology Letters, "as we did not observe any attempts by the fishes to feed on the shrimps.
"Both species were clearly attracted by the fishes, walking on them and examining various parts, including the mouth region. They used their pincers in a manner indicating that they were feeding on dermal ectoparasites.
"Interestingly, the fishes did not make any attempt to feed on the shrimps, suggesting a symbiotic relationship similar to that seen on coral reefs."
The Plaice and shrimps were kept together in aquariums at Klubban Marine Station in Sweden where the team monitored their behaviour and periodically analysed the number of parasites on their skin.
They also analysed the gut contents of the shrimps to prove that they had eaten the parasites: all of the shrimps had consumed Gyrodactylus flukes on the skin of the Plaice.
The authors believe Palaemon shrimps, which live in seaweeds, might also perform a similar role on fishes that live above the seabed and within the algae belt.
"The results raise the possibility that these highly abundant shrimps can be used as cleaners in aquaculture, where ectoparasites can have a significant negative impact", the authors concluded.
For more details see the paper: Ostlund-Nilsson S, Becker JHA and GE Nilsson (2005) - Shrimps remove ectoparasites from fishes in temperate waters. Biology Letters, Volume 1, Number 4 / 22 December 2005, pp. 454-456.