“Freeze-or-Flight” Reactions Happen in Families of Fish – ScienceDaily


Families of fish tend to share similar reactions to stressful situations, new research shows.

Scientists from the University of Exeter examined how Trinidad guppies reacted to stress: did they freeze or flee? — and also measured their hormonal responses.

The study found that some fish tend to produce more cortisol, a hormone, and these fish are more likely to flee, while others produce less cortisol and tend to freeze. This pattern runs in families.

The results could aid in the breeding of less stressed fish for aquaculture (fish farming) and other captivities such as aquariums.

“In the wild, an instinct for flight can help a fish escape danger, and a surge in cortisol helps them cope with that stress,” said lead author Dr Tom Houslay of the Center for Ecology and Conservation (CEC) on Exeter’s Penryn. Campus in Cornwall.

“But in captivity, this reaction is unnecessary – a chronic high cortisol stress response is harmful to health and well-being.

“Our finding of a genetic link between hormonal (cortisol) and behavioral (freeze or flight) responses suggests that fish could be selected for breeding based on their freezing or flight response.

“By selecting fish that tend to freeze in a stressful situation, you create a genetic stock with a lower cortisol stress response.”

This approach is simpler than other breeding methods, some of which rely on a blood sample to identify genetic patterns.

“We need to stop thinking that fish are all the same,” said Professor Alastair Wilson, also from the CEC at the University of Exeter.

“Individuals and groups of close genetic relatives vary, and by taking this into account, we can selectively breed captive fish with less stress and better health.”

Biologists have long believed that this “integration” of behavioral and hormonal responses must exist, but few formal genetic tests have been performed.

In this study – led by a team including the University of Alabama – researchers tested hormonal responses by placing individual guppies in isolation for an hour. For a social fish like the guppy, handling and isolation is likely to be a mild stressor.

During a stress response, high levels of cortisol help shift the energy balance of the body in order to cope with the stressor. This aids recovery and prepares the body for any further stressors. Cortisol is a necessary element to deal with stress, but if this response is used too frequently, it can lead to health problems.

Cortisol escapes through guppies’ gills, so their hormones were measured by testing the water after they returned to their usual tank.

Behavior was tested separately, also by placing each guppy in a new tank, and seeing if they tended to stay still (freeze) or swim trying to escape (flee).

Hundreds of fish were observed in the study, and the researchers looked at each one’s “family tree” to see how genetic relatedness correlated with behavioral and hormonal similarities.

The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

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Material provided by University of Exeter. Note: Content may be edited for style and length.

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