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What Water Temperatures Can Cod Handle?

25 February 2011

DENMARK - Hundreds of cod equipped with high-tech mini-thermometers have helped determine which water temperatures the fish can handle.

Cod are traditionally regarded as fish that thrive in cold water, and therefore represent a species that might find things hard going in a future climate change with rising sea temperatures.

Now for the first time and using modern advanced technology, it is possible to examine exactly at which temperatures cod are found in the Northeast Atlantic.

Researchers from several European universities, among them the National Institute of Aquatic Research in Denmark (DTU Aqua), equipped more than 2000 cod from eight different North Atlantic stocks, including the Baltic, the Skagerrak and the North Sea, with advanced temperature gauges. For over a year the gauges registered and stored water temperatures around the fish at fixed regular intervals. The results have just been published as a feature article in the "Marine Ecology Progress Series."

"It's absolutely unique to have data from such a large and comprehensive study," says Professor Ken Haste Andersen, one of four DTU Aqua researchers who participated in the international project.

The project has concentrated on cod because it is such an important fish commercially; at the same time, it is a large fish which can easily carry the electronic tag without being bothered by it.

The results indicate that adult cod can handle much warmer water than was originally thought.

"Some fish were found at temperatures as cold as -1.5 degrees, while others swam quite happily in water that was nearly 20 degrees above zero. This shows that cod are relatively adaptable fish that can tolerate higher temperatures than was previously thought. However, while this is true for adult cod, they appear to be somewhat more conservative in their choice of water temperature when they spawn. During this period, all the fish stocks studied consistently sought out water that had a temperature of between one and eight degrees. This indicates that the egg and larvae stages of a cod’s life may constitute a particularly vulnerable time with regard to the effects of climate change," says Professor Andersen.

However, the fact that cod in the Northeast Atlantic can survive in water temperatures which fluctuate up to 20 degrees does not mean that all adult cod can tolerate all temperatures. If you took a cod from the North Sea and moved it to the -1.5 degree water north of Iceland, the coldest water measured in the survey, it would be seriously challenged.

"Each fish stock in each area is well-adapted to the local conditions. It is widely known that cod can live in water at subzero temperatures, because they can produce antifreeze proteins which protects them," says Professor Andersen from DTU Aqua.

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