Quirks & Quarks

Amphibious fish out of water get a brain boost from exercise

Researchers put amphibious fish through a land-based exercise program and found they got smarter and their brains grew. This may help explain what happened when our ancestors left the oceans hundreds of millions of years ago.

New study shows that the fish get smarter, bigger brains after exercising on land

A mangrove rivulus jumps as a part of a vigorous terrestrial workout. These amphibious fish can live for up to 2 months out of water. (Brock Fenton)

Researchers have found that amphibious fish gain a brain boost after going through a vigorous exercise routine outside of the water.

"It's a fish out of water. It just seems so counterintuitive, but it's really helpful for these fish," biologist Giulia Rossi told Quirks & Quarks host Bob McDonald.

There are 11 different major groups of amphibious fish, spanning hundreds of species, which can live in both water and on land.

"Some species can tolerate air exposure for a few minutes and others for several months," said Rossi. "Some species breathe through the skin … [while] others have lungs and other air-breathing organs."

A mangrove rivulus is seen leaping from puddle to puddle. (Keri Martin)

And while much research has been done on the physical attributes of these fish, Rossi wanted to know what these adaptations could do to the animals brains. 

The results were published in the journal Proceedings of the Royal Society B.

Fishy workout sessions thanks to a boop to the nose

Rossi's team at the University of Guelph worked with three groups of mangrove rivulus, a killifish which can survive for up to two months on land.

The first group was kept in water for the entire experiment. The second group was plucked out of the water at random intervals and for random lengths of time. The third group was regularly removed from the water for a vigorous exercise session.

"We actually put fish in this really big arena, if you want to call it that, and we use a little clicker ballpoint pen to deliver a stimulus right to their nose, so we were able to give them a gentle but consistent poke," said Rossi. The fish were able to jump several body lengths into the air after being poked, and went on until the researchers felt they had gotten a good workout.

A mangrove rivulus fish can leap several body lengths in the air when provoked. (Brock Fenton)

After eight weeks, she put the fish through a maze for 10 consecutive days, and found the fish that had been exercised, as well as the group that had been randomly exposed to air, performed significantly better than the group that had just been in water, learning the most efficient route through the maze and finding the food quicker overall.

They may be good models for understanding how our fishy ancestors struggled onto land the first time.- Giulia Rossi

To gain a better understanding of what was happening, she then examined  the fish brains, and could see physical changes were taking place. She found that in the areas of the fish brains responsible for spatial cognition, the animals from the air-and-water and exercise groups had more proliferating or dividing cells in the brain, a process called neurogenesis.

"Fish have a huge capacity for neurogenesis, so lots of different regions in their brain can actually form new neurons. Fish are really good at it. Other vertebrates like humans [are] actually not that great at doing that," said Rossi.

Understanding evolution

Rossi said that the studies mirror what we know about human brain development.

"We know that exercise is really important for cognition, but even being in new environments is really important," she said. "Fish out of water are experiencing novel stimuli like rain or wind or terrestrial predators. So there's lots going on if you're moving between aquatic and terrestrial environments."

The mangrove rivulus fish, as the name suggests, is typically found in areas with Red Mangrove trees, like Florida, Mexico and Brazil. (Dr. Andy Turko)

She believes the results can also give insights into how the aquatic ancestors of all land vertebrates moved onto land 400 million years ago.

"They may be good models for understanding how our fishy ancestors struggled onto land the first time," she said. "The first fish that moved out of water, if they had this greater capacity for learning, they may have been more successful in a terrestrial environment," she said.


Produced and written by Amanda Buckiewicz.

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