Fish can succumb to heatstroke, too

Fish can adapt to rising sea temperatures, but only to a certain degree. There is a risk that entire populations may die out as the climate changes. And it’s probably the fish’s heart that determines how high a temperature a fish can tolerate. This is borne out by new research from the University of Gothenburg.

The ongoing global warming trend brings not only elevated temperatures but also extreme heat waves. Among other things, this affects oceans and lakes and the fish that live there.

In his doctoral thesis Andreas Ekström, a researcher at the University of Gothenburg, has investigated how much heat fish can put up with. Studies show that when ocean temperatures increase, certain fish populations move northward towards cooler waters. Other species that are not as mobile must stay and endure climate changes. For these species, an extreme heat wave is enough to exterminate an entire population of local fish.

‘Today we do not know exactly what determines the heat tolerance of fish, but much suggests that their hearts play a central role’, says Andreas.
If the water temperature rises too much, the fish’s heart can completely cease functioning, with deadly consequences. But why is this? ‘It may be partly because the heart’s own supply of oxygen is limited when it gets too warm. This, in turn, could lead to an inability of the heart to pump enough oxygen-rich blood to the body.’

A LARGE PART of Anders Ekström’s research has been conducted at the Biotest enclosure in the archipelago outside the Forsmark nuclear power plant. This artificial enclosure is a unique research environment because for decades cooling water from nuclear reactors has been pumped out into a one-square-kilometre enclosed area in the archipelago. It has raised the water temperature by 5-10 ° C compared to the surrounding Baltic Sea water.

Studies indicate that perch in the heated Biotest enclosure are not as heat-sensitive as perch in the cooler archipelago. The differences in thermal tolerance depend both on the fact that hearts of fish in the Biotest enclosure pump better at high temperatures and that the fish have developed a more efficient way to convert energy in the heart compared to other perch.

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