Fish have a massage to reduce stress

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What do coral reef fish do when they are stressed? They go for a nice, relaxing massage, according to research published in a recent issue of the journal Nature Communications.

Marta Soares and coauthors found that stress levels in the Striated surgeonfish (Ctenochaetus striatus) are significantly lowered when they had their fins rubbed in a manner that the Bluestreak cleaner wrasse (Labroides dimidiatus) would do while cleaning them.

The authors constructed eight cleaner wrasse models with a soft brush on their undersides. Four of these models were rigged so that they would rock back and forth and the four were fixed in place and left stationary. For ten consecutive days, the authors exposed four surgeonfish to the moving model and the other four to the stationary model, with each encounter lasting an hour and being carried out twice per day (once in the morning and once in the evening). Fish behaviour with the models was recorded on the tenth day.

The authors then extracted blood from the fish on the eleventh day to measure their cortisol levels; as cortisol is a stress hormone, its level in the blood is a useful proxy for the level of stress that the fishes are experiencing. Before blood extraction, the authors exposed half of the fish in each treatment to a confinement stress (by placing them in a bucket with a reduced amount of water in it) The authors additionally evaluated whether cortisol levels were correlated with the time surgeonfish spent interacting with the moving model.  

The authors found that the surgeonfish exposed to the moving models touched and interacted with them more frequently (the surgeonfish were able to position themselves beneath the moving model such that the model rubbed against their bodies).

They also found that the surgeonfish exposed to an acute (confinement) stress that had access to moving models, had lower cortisol levels the more time they spent interacting with models.

This is the first time that physical contact in the absence of a social factor (ie. a massage) has been shown to reduce stress in an animal other than humans, the authors claim.

"Humans go to have massages when we feel sick or just to feel better, so maybe the reasons are basically the same," said senior author Marta Soares.

For more information, see the paper: Soares, MC, RF Oliveira, AFH Ros, AS Grutter and R Bshary (2011) Tactile stimulation lowers stress in fish. Nature Communications 2, 534, doi:10.1038/ncomms1547.

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