Tactile stimulation lowers stress in fish

In humans, physical stimulation, such as massage therapy, reduces stress and has demonstrable health benefi ts. Grooming in primates may have similar effects but it remains unclear whether the positive effects are due to physical contact or to its social value. Here we show that physical stimulation reduces stress in a coral reef fi sh, the surgeonfi sh Ctenochaetus striatus . These fi sh regularly visit cleaner wrasses Labroides dimidiatus to have ectoparasites removed. The cleanerfi sh infl uences client decisions by physically touching the surgeonfi sh with its pectoral and pelvic fi ns, a behaviour known as tactile stimulation. We simulated this behaviour by exposing surgeonfi sh to mechanically moving cleanerfi sh models. Surgeonfi sh had signifi cantly lower levels of cortisol when stimulated by moving models compared with controls with access to stationary models. Our results show that physical contact alone, without a social aspect, is enough to produce fi tness-enhancing benefi ts, a situation so far only demonstrated in humans.