According to a study published in the Journal of Experimental Biology, fish exposed to warmer water would have a bigger, but less efficient brains.

The more our knowledge of global warming grows, the more we become aware of the extent to which it can disturb global ecosystems. We already knew climate change makes extreme weather events more frequent, while affecting the capacity of forests to store carbon and produce oxygen, which then contributes to ocean acidification…

But a new study published in the Journal of Experimental Biology suggests adding a new item to the list of consequences of global warming: it might affect the brains of fish. Further explanations right ahead.

Global Warming Affects The Brain Of Fish

Researchers wanted to know how rising temperatures in freshwater rivers and lakes could affect fish development and metabolism. In order to find this out, they studied how minnows, fish of the Cyprinidae family, the most common fish family in freshwaters.

Minnows are used to water around 14 degrees and researchers studied how they reacted when exposed to warmer water. More precisely, the fish were exposed to water temperature around 20 degrees – the expected freshwater temperature in the northern hemisphere in the event of pronounced global warming. The result?

Fish raised in warmer waters developed, on average, larger brains. In particular, the long marrow region appears to be more developed in fish raised in warm water than the others. But surprisingly, this brain development might be a sign of a less efficient brain.

Warmer Waters Increase Fish Metabolism

The researchers also noticed that fish raised in warmer water had a harder time than others in carrying out certain tasks. In particular, they were less successful in locating their food in a labyrinth. This means they are likely to find it harder to orient themselves and to identify and reach prey in open waters.

The explanation for this might come from a metabolic change. In fact, the overdeveloped brain area – the long marrow – in fish raised in warm water is the area responsible for a certain number of autonomous metabolic functions: heart rate, regulation of blood pressure, oxygenation, etc.

It is likely that the development of this brain area is a sign of a higher metabolic demand for warm water. In other words: living in warm water is more demanding for fish since it spends more energy and contributes to developing the long marrow in the brain. 

Moreover, this energy consumed for metabolic purposes is then no longer available for other areas of the brain, responsible for more developed cognitive functions, such as orientation.

Global Warming and Larger Fish Brains: Ecosystemic Implications

This study is among the first that identify the profound physiological modifications the change in water temperature can have on fish and biodiversity. And if these impacts may seem, a priori, unimportant, the fact is that they bring along the potential for larger, systemic consequences on the whole chain of ecosystems of which fish are a part of.

In fact, fish having more difficulty orienting themselves or finding their prey could quickly lead to a populational fish decrease or put survival at risk in certain ecosystems. Under circumstances, entire food chains can potentially be modified.

Other studies on fish have thus highlighted the size changes induced by global warming could disrupt marine food networks and food chains. In ecosystems already deeply modified by human activities, and which will be further affected by global warming, such a discovery is far from trivial.

[Photo by Sebastian Pena Lambarri on Unsplash]