Do fish get lonely? Damselfish get stressed and lose weight when separated from their shoals on coral reefs just like in Finding Nemo

  • Damselfish living alone lose weight, reducing their chance of survival
  • Their metabolic rate also increases indicating they are suffering stress
  • Researchers say socialising in shoals appears to have a calming effect
  • Coral reef fish can become separated from shoals by powerful storms 

For the characters in the Disney movie Finding Nemo, being separated from their family and friends was a frightening experience.

But it seems that real fish living on coral reefs also become stressed out and even lose weight if they are separated from each other.

A new study suggests fish that live around coral reefs have a lower chance of survival if they get separated from their shoal mates.

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Blue-green damsel fish (pictured) gather in shoals of more than 1,000 strong around coral reefs, but if they are separated from others in the shoal they can lose weight and show signs of stress. The findings suggest that fish may be far more social than previously believed

Blue-green damsel fish (pictured) gather in shoals of more than 1,000 strong around coral reefs, but if they are separated from others in the shoal they can lose weight and show signs of stress. The findings suggest that fish may be far more social than previously believed

The findings also indicate that fish may be far more social creatures than perhaps previously realised and can get lonely when they are by themselves.

CORAL DEATH AFFECTS FISH

Researchers have found that coral bleaching and death can have dramatic repercussions for how small reef fish learn about and avoid predators.

The finding is not only bad news for the fish but the reef itself, because it could prevent the living colonies replenishing.

The study, published in Proceedings of the Royal Society B, found coral death and degradation affects how a common damselfish responds to the tell-tale chemicals that indicate the presence of hungry predators.

When corals die and become covered in algae, the olfactory landscape of the reef seems to change, which affects this crucial learning mechanism used by fish.

The Australian-Swedish research team found that the smell of an injured mate paired with a predator taught the ambon damselfish to learn to avoid new predators when on live coral, while their counterparts on dead coral didn't respond to or learn any predator cues. 

Lauren Nadler, a marine biologist at James Cook University in Queensland who led the study, said when they isolated blue-green damsel fish from the Great Barrier Reef they lost weight.

The fish were also found to have a higher metabolic rate than those who were able to socialise in their shoals.

Miss Nadler said: '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.'

Damselfish are usually found in shoals that can be more than 1,000 fish strong but can become separated from each other in bad weather or by predators.

The researchers captured fish living on the Great Barrier Reef and separated them from the rest of their shoal so they could monitor what happened to them.

They found those who were in shoals tended to be calmer and had a 26 per cent lower metabolic rate than those living alone.

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

'Fish were calmer and less stressed when they had their shoal-mates around.' 

The findings suggest that damselfish (pictured) and other coral dwelling species may get lonely if they are separated from their shoals by storms

The findings suggest that damselfish (pictured) and other coral dwelling species may get lonely if they are separated from their shoals by storms

The researchers first began noticing that fish separated from their shoals (pictured) by storms were struggling to survive. They say the extra stress of looking out for predators while foraging for food makes it harder for them to survive

The researchers first began noticing that fish separated from their shoals (pictured) by storms were struggling to survive. They say the extra stress of looking out for predators while foraging for food makes it harder for them to survive

Last year, parts of the Great Barrier Reef were hit by powerful winds and bad weather from Cyclone Nathan and researchers began noticing blue-green damselfish living by themselves.

The researchers, whose work is published in the Journal of Experimental Biology, believe that such events can have a dramatic impact on the survival of the species.

Professor Mark McCormick, a coral reef ecologist at James Cook University, 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.

'Since they don't have their buddies around to help look out for looming predators, foraging for food would be riskier.

'The extra energy fish gain from shoaling is so important because it allows them to survive and reproduce and to pass on their genes to the next generation of fish.' 

The research suggests that Disney's depiction of a fish that gets separated from his family in Finding Nemo (pictured) may not have been completely inaccurate as fish do get stressed when alone. Clown fish like Nemo, however, tend to live in pairs rather than large shoals

The research suggests that Disney's depiction of a fish that gets separated from his family in Finding Nemo (pictured) may not have been completely inaccurate as fish do get stressed when alone. Clown fish like Nemo, however, tend to live in pairs rather than large shoals

The findings could shed light on how coral reef fish (pictured) are able to survive following major storms or other events that can lead them to get separated from their shoals 

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