‌The steroid hormone cortisol regulates many important bodily functions and plays a crucial role in the adaptive response to stress, and is therefore often referred to as the “stress hormone”.

We know that people with strong bonds, like romantic couples, or parents and their children, coregulate their cortisol levels.

This means that cortisol responses in partners or parents and children quite often match one another, which likely is important for health and relationship functioning.

Whether cortisol coregulation also exists in non-human animals that lack strong bonds was unknown.  But Dr Fürtbauer, who is based in the University’s College of Science, suspected that cortisol coregulation might not be unique to humans, but instead something that may occur in social vertebrates, more generally.

Dr Fürtbauer examined cortisol coregulation in pairs of stickleback fish and adopted an experimental set up similar to that used by psychologists studying human subjects.

First, fish were paired and housed together, which is equivalent of being “at home” in the human studies. Then, the fish were put into a new tank (a challenging situation) several times, either by themselves (equivalent to being “at work” in the human studies) or with their pair partner (equivalent to “sharing distress” in the human studies).

Cortisol levels were measured non-invasively from water samples which were collected from each fish after each experience.

The researchers found that fishes’ cortisol levels were unrelated when they were in their home tanks, but correlated positively when sharing a more stressful environment.  

This finding is similar to studies on humans that find cortisol coregulation is stronger in distress situations. It also provides the first evidence that cortisol coregulation is not unique to humans, as Dr Fürtbauer suspected.

“Our study shows that non-humans living in less-bonded societies can coregulate each other’s stress physiology,” said Dr Fürtbauer.

“Our findings suggest an adaptive function of cortisol coregulation during challenging situations, which might include, for example, the mitigation of risk.”

Now that Dr Fürtbauer has found evidence for cortisol coregulation in fish, her team are currently investigating how and over what time-frame this happens, both of which are difficult to study in human subjects.

A copy of the full paper – Fürtbauer, I. & Heistermann, M. (2016) Cortisol coregulation in fish. Sci. Rep. 6, 30334; doi: 10.1038/srep30334 – can be found here.