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Fish have a stress response that runs in the family

The way some fish respond to stress seems to run in the family, according to new research from the University of Exeter. The scientists observed Trinidadian guppies under stress and measured their hormone levels. The research shows that when a fish produces more cortisol, the individual is more likely to flee. On the other hand, when a fish produces less cortisol, the animal is likely to freeze in place. 

“In the wild, an instinct to flee can help a fish escape from danger, and a rush of cortisol helps them cope with that stress,” said lead author Dr. Tom Houslay of the Centre for Ecology and Conservation (CEC) on Exeter’s Penryn Campus. “But in captivity, this reaction is unhelpful – a chronic, high-cortisol stress response is harmful to health and welfare.”

The scientists hope their research may ultimately be useful in breeding more stress-free fish for farms and other captive situations such as aquariums. 

“Our finding of a genetic link between the hormonal (cortisol) and behavioral (freeze or flee) reactions suggests fish could be selected for breeding based on their freeze or flee response,” said Dr. Houslay. “By selecting fish that tend to freeze in a stressful situation, you create a genetic stock with a lower cortisol stress response.”

This is similar to methods already in use for fish breeding that rely on blood sampling to select desired traits. This technique relies on the diversity of fish behavior, which is something most people don’t consider when looking at fish behavior. This works because fish are actually unique individuals with some heritable behavior. 

“We need to stop thinking of fish as being 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 account of this we can selectively breed captive fish with lower stress and better health.”

The study is published in the journal eLife.

By Zach Fitzner, Staff Writer

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