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The mystery of the curious Crucian carp

Crucian carp (Carassius carassius) from a pond near Oslo. Image courtesy of Göran Nilsson.
Click here for a high resolution photograph.

Most animals can only live for minutes without oxygen -- just try holding your breath and see how long you can go. But, the crucian carp, which is related to the goldfish, can survive for several days with almost no oxygen.

The ability to live in these conditions allows the carp to last through the winter in the shallow, ice-covered ponds of Scandinavia. Scientists still don't know exactly how these unusual fish do this, but they've discovered that a hardy heart rate is at least part of the answer.

The researchers describe their findings in the 1 October issue of the journal Science.

A small handful of animals, like freshwater turtles and common carp, can also survive without much oxygen. They do it by drastically slowing down their heart rate and other systems inside their bodies.

This way, the animals don't produce many waste products that can harm the body in large amounts. Lactic acid is an example of one of these waste products. (Small amounts of lactic acid are what make your muscles feel sore after they've worked hard.)

The crucian carp survives prolonged periods without oxygen while maintaining normal heart function. Image courtesy of Göran Nilsson.
Click here for a high resolution photograph.

Unlike the turtles, however, the crucian carp stays active in its low-oxygen environment in winter. Scientists do know that the fish gets around the waste problem by converting the lactic acid to ethanol, which is much less harmful. Ethanol is actually a form of alcohol though, so the fish does eventually need to pump the ethanol out of its system.

Jonathan Stecyk of the University of British Columbia and his colleagues wanted to know more about this odd fish, so they collected their fish nets and traveled to Oslo, Norway. They spent two days pond-fishing from a little rubber dinghy and caught some crucian carp to take back to their laboratories.

"I'm trying to understand why these animals can do this amazing feat," Stecyk said.

The researchers discovered that the fish actually kept their hearts pumping normally, even when swimming for five days in water that had little oxygen and was a chilly 8 degrees Celsius (46 degrees Fahrenheit). Stecyk's team thinks that this hardy heart pumping may help circulate the ethanol to the fishes' gills, where it can flow out of the fish and into the water.

Stecyk explained that heart attacks and strokes can cause humans to die because their hearts and brains don't get enough oxygen. To him, that makes it especially remarkable that crucian carp's heart can pump with hardly any oxygen. He hopes that his research might someday give other scientists ideas about how to help people who are having heart attacks or strokes.


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