Fish brains grow and shrink according to their mental activity

An integrative biologist at the University of Guelph in Canada, Frederic Laberge, focused on the brain size of fish and how it benefits them, especially given that it is known that the brain is one of the most Tissues that are expensive to maintain.

In a study published on BioRXiv, Laberge's team compared the brain sizes of rainbow trout, which live on a fish farm in Parry Sound, Ontario, to those that came out of a hatchery and were living in the wild in a nearby lake.

After seven months, the brains of wild trout were 15 percent heavier than that of captive trout, relative to their body size. The growth spurt was limited to the gray matter, Laberge told New Scientist and did not affect their heart or other organs. His theory is that more complex living environments force fish to literally increase their brainpower.

Laberge adds that fish brains are flexible and can grow larger when faced with more complex environments. But change isn't always necessary. In another study, published on Authorea, Laberge studied trout in two lakes in Ontario over several years.

He found that their brain size increased in the fall and winter, then decreased in the spring and summer. The lake trout actually prefer cooler waters, so when the cold season starts in the lake, they can get food closer to the surface and shore. This creates a more competitive and complex environment for them, says Laberge, which requires more gray matter.

Previous research by Laberge found that the brains of sunfish in coastal habitats were larger than those of their open water counterparts. According to a 2018 study published in Proceedings Of The Royal Society B, all fish were equally healthy and with similarly sized heads.

But the brains of the coastal (shore) sunfish were, on average, 8.3 larger than those of the aquarium (open water), although not one brain area was larger than another.

Co-author Caleb Axelrod said in a university, Habitat is already having an impact. Coastal fish may be better at adapting to the increasing issues of pollution and climate change because they already have more cognitive abilities.

Scientists have demonstrated that fish in labs have smaller brains than their free-range cousins, but Laberge's work is the first to show such a variance in the wild.

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