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Global Ideas

Damselfish in distress

Coral reef fish don't like getting separated from their 'shoal-mates,' new study finds.

Coral reef fish prefer company. The fish get stressed out and lose weight if they are separated from each other, affecting their ability to survive, a study published Thursday has found.

Scientists at the James Cook University studied Damselfish captured from the Great Barrier Reef to find out why they preferred to socialize by isolating some and keeping others together in shoals.

"The fish that were isolated lost weight after the first week, which meant they were less healthy than those in groups," lead study author Lauren Nadler said in a statement.

The team of scientists measured the metabolic rate - which is an indicator of stress - in fish both in a shoal and alone and confirmed what they had suspected: staying in groups had a "calming effect."

"Fish were calmer and less stressed when they had their shoal-mates around, with a 26 percent decrease in metabolic rate compared to individuals tested alone," said Nadler.

Natural disturbances such as tropical cyclones can sometimes disperse the shoal-mates. But by sticking together fish don't burn through energy as quickly, which helps them to stay alive and reproduce.

"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," said study co-author Mark McCormick in the statement. "Since they don't have their buddies around to help look out for looming predators, foraging for food would be riskier."

The results of the study published in the Journal of Experimental Biology show how important group living is for healthy fish populations, say the scientists.

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