Coral Fish Are Less Stressed When They Find Their Shoal Mates


Katy Evans

Katy is Managing Editor at IFLScience where she oversees editorial content from News articles to Features, and even occasionally writes some.

Managing Editor


Damselfish swim in shoals of up to 1,000 fish. Eva McClure/James Cook University

Nobody wants to be alone, which is why as humans, we are fascinated by the idea of soul mates. According to new aww-inducing research, the same is also true for coral fish, although it's "shoal-mates" not soul mates they're searching for. 

According to the study, published in the Journal of Experimental Biology, coral fish get stressed and lose weight when separated from their shoal-mates, affecting their chance of survival.


"We have suspected that shoaling fish gain a 'calming effect' from living in a group. But up until now we have been unable to measure how widely spread this effect is in individual fish," said Lauren Nadler, lead author of the study from James Cook University, in a statement.

Nadler and her team from the ARC Centre for Excellence for Coral Reef Studies in Queensland, Australia, set out to discover how important group living is for healthy fish populations after Cyclone Nathan, a category 4 cyclone, passed over Lizard Island on the Great Barrier Reef last year.

They noticed several damselfish – a blue-green coral-dwelling fish often found in thousand-strong shoals – living on their own on small coral colonies, apparently having been separated from their shoal by the storm and currents.

Many animals live in groups for varying reasons that prove beneficial, such as protection, feeding, and reproducing. Group living can also produce what is called a "calming effect", which according to the authors reduces metabolic demand (a sign of stress) by “minimizing the need for individual vigilance and reducing stress through social buffering.”


To study them, the team captured shoals of the damselfish and then isolated some whilst keeping others in their shoals. The metabolic rate of the fish were then measured after one week.

The results showed that the isolated fish lost weight, meaning their metabolic rate had gone up in response to the stress of being alone. Meanwhile the fish in shoals had a 26 percent decrease in metabolic rate compared to the lone fish.

“The fish that were isolated lost weight after the first week, which meant they were less healthy than those in groups,” Nadler said.

"If these fish were out in the ocean by themselves, in order to stay alive they would need more food to keep up their energy," co-author Mark McCormick added. "Since they don't have their buddies around to help look out for looming predators, foraging for food would be riskier."


The study concluded that shoal fish living on their own expended more energy on trying to survive and that “social isolation as a result of environmental disturbance could have physiological consequences for gregarious species.” The researchers hope to conduct more studies to determine the long-term effects of separation on other species.

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  • stress,

  • Great Barrier Reef,

  • damselfish,

  • social isolation,

  • shoaling,

  • metabolic rates