Pairs of cleaner wrasses work together to give better service on the coral reef

In an article in the latest number of the scientific magazine Nature researchers from Stockholm University have studied how certain fish on the coral reef keep other species of fish clean.

The Bluestreak cleaner wrasse (Labroides dimidiatus) helps other fish species by eating parasites from their skin. The cleaner wrasse's favourite food is, however, the nutrient rich mucus layer that covers the client fish.

Bluestreak cleaner wrasses eat parasites that have attached themselves to the client fish – but sometimes the cleaner wrasses can't resist the temptation to take a bite out of the client's mucus layer.

“As it's a painful pinch the client fish ends the co-operation, shakes off the cleaner wrasse and swims away,” says Olof Leimar, professor at Stockholm University's Department of Zoology, and leader of the research project.

The cleaning is sometimes carried out by a single fish and sometimes by a pair of fish that together service the same client. The question is if a pair of fish gives better or worse service than a single cleaner wrasse.

“We used a combination of methods – including theoretical models, field observation, and laboratory experiments – in order to map the differences between when the cleaner wrasses work alone or in pairs. Our theoretical model indicates that as long as the cleaner wrasses co-operate and watch each other's behaviour they abstain from taking that tempting bite. In such cases the service for the client fish is better than when the fish work alone. Our field observations and laboratory experiments have shown the same results,” says Olof Leimar.

Another interesting dimension is that the pairs always consist of a male and a female – and that the female contributes more than the male to the improved level of service.

“The pattern of behaviour between females and males needs to be studied. The males are larger than the females. If the female takes a forbidden bite the male will often chase the female. This could mean that the different bodily strengths within the pair lead to a repressive situation with the threat of punishment,” says Olof Leimar.

For further information contact Olof Leimar, professor, Department of Zoology, tel: 08-16 4056, mobile: 070-285 09 93, email: Olof.Leimar@zoologi.su.se

Image: A pair of Cleaner wrasses (Labroides dimidiatus) clean a Surgeonfish (Acanthurus mata) (640 x 446px 104Kb)

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