By Rachel Baxter
Goldfish and their wild crucian carp relatives can survive for five months without breathing oxygen – and now we know how. The fish have evolved a set of enzymes that, when oxygen levels drop, ultimately helps convert carbohydrates into alcohol that can then be released through the gills.
For most animals – including humans – a lack of oxygen can be fatal within minutes. We can metabolise carbohydrates without oxygen, but the process generates toxic lactic acid that quickly builds up in our bodies.
On the face of it, this should pose a big problem for crucian carp. They live in ponds and lakes in northern Europe and Asia that freeze over in winter, so the fish have to survive for months without oxygen until the ice melts in spring.
But the carp – and their close relative the goldfish – have developed a workaround. When they metabolise carbohydrates anaerobically, the end product is not lactic acid but alcohol, which is easier to remove from their bodies.
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