Experiments with fish have shown that it isn’t just humans that get health benefits from a massage.

In humans, massage helps to lower stress. This can be tested by measuring levels of substances like cortisol in the blood. If a person is stressed, their levels of cortisol increase.

Now, scientists have found that contact similar to a massage can help to lower the levels of cortisol in reef fish too.

Reef fish often go to specific areas of the sea called cleaning stations, where smaller cleaner fish will pick off any parasites from the reef fish’s body. However, the cheeky cleaner fish often cheat at their jobs and eat mucus from the fish’s body instead. Although the cleaner fish much prefer to eat mucus, the reef fish don’t get any benefit from this, and often start conflicts with the cheats.

When these conflicts start, the cleaner fish often swim onto the reef fish’s back and lightly massage it with their fins.

Scientists reproduced this bizarre process in the lab, using a fake cleaner fish. The dummy fish was either kept still or timed to move gently back and forth, so that the reef fish could get a massage from it.

The fish that got a massage saw their cortisol levels drop compared to the other fish. Scientists now think that cleaner fish have developed their massage technique to make up for the times when they cheat at their cleaning job.

To see a cleaner fish in action, check out the video below.