Fish brains bigger in warm water, but study reveals size matters not

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This article was published 20/05/2020 (2008 days ago), so information in it may no longer be current.

Climate change appears to have the ability to make small fish grow larger brains, with less going on in them, according to new research done by biologists at the University of Glasgow.

A team of biologists took minnows and monitored the physiological effects of warmer water on their development over the course of eight months, then observed changes in behaviour. They reported minnows that lived in the warmer water developed brains approximately 20 per cent larger, but were less effective when it came to exploring their surroundings and finding food.

“Although we found their brains were larger, they seemed less able to accomplish the simple tasks that minnows carry out every day,” said Libor Zavorka, lead researcher on the project.

Researchers at the university’s Institute of Biodiversity Animal Health and Comparative Medicine fished the minnows out of the nearby River Kelvin. They placed one set of fish into water kept at 14 C, and another set in water warmed to 20 C.

The former reflects the typical temperature of the river locally, while the latter reflects the temperature the river reaches during heat waves and is also expected to be the typical temperature of the Scottish river by the end of the century if climate change continues unabated.

Fish were then tested in mazes to see which group was more successful in locating food.

“The funny thing is that the increase (in the size of the fish brains) didn’t have any effect on their cognitive skills; in fact, they did worse in the maze test than the fish from the cool water. Which is challenging the idea put forward in quite a lot of research — particularly in fish — that with a bigger brain, you have more cognitive capacity,” Zavorka told the Free Press.

He said he believes other research indicates the number of neurons and the biochemical composition of the brain is more critical than size, perhaps is bearing out in this research.

“In this study, we didn’t look at any of those parameters, we looked at just the volume (of the brains) and our results clearly show that the size of the brain is not a good representation of cognitive skills — because they had bigger brains, but they were actually more stupid.”

“Although we found their brains were larger, they seemed less able to accomplish the simple tasks that minnows carry out every day.”
– Libor Zavorka, lead researcher

The metabolism of cold-blooded fish depends on their environment, Zavorka said — the warmer it gets, the faster their metabolism.

There would be a limit to how much a species could adapt before it starts dying off. In the case of the minnow, however, Zavorka believes the fish will be able to adapt to their new environments for the most part, but the research demonstrates a cost of that adaptation, as there would also be spinoff effects throughout the ecosystem.

Zavorka said the Glasgow group chose to use a minnow because the family of fish is common all around the world.

Researchers have only begun to scratch the surface of the complex effects climate change will have of fresh-water species. Zavorka said he expects impacts on these diverse ecosystems will be felt sooner and to a greater degree than the species living in saltwater, as seas and oceans are typically deeper and will warm slower than lakes and rivers.

Research done at the Experimental Lakes Area, located about 70 kilometres east of Kenora, Ont., has shown warming water over time is impacting the size of larger species of fish such as Lake Trout, with researchers there predicting the southern range of the fish will slowly creep northward. Similar research has documented this phenomenon in Atlantic cod.

“But in the sense of how other traits of the animals’ behaviour will be effected, that’s pretty much unknown, and, of course, this is a really important part because the way they behave or their cognitive skills will affect their capacity to find food or avoid predators or survive and reproduce,” Zavorka said.

“… our results clearly show that the size of the brain is not a good representation of cognitive skills– because they had bigger brains, but they were actually more stupid.”

The next step in the Glasgow research will involve observing how fish in warmer water behave in the wild, as a laboratory setting doesn’t give researchers a sense of other adaptation measures the fish might take on to counter the change in temperature, such as moving to deeper waters.

sarah.lawrynuik@freepress.mb.ca

Twitter: @SarahLawrynuik