Thursday, 18 July 2013

Crucian carp: wintering without oxygen

When dissecting crucian carp - as you do - don't be surprised if your specimen is a little livelier than you'd expect for a head disconnected from the heart for several hours. Crucian carp (Carassius carassius) are remarkably able to survive totally anoxic conditions (without oxygen).

Their secret is anaerobic respiration - releasing energy without needing oxygen. Though it's 15 times less efficient than aerobic respiration (with oxygen), which is what animals normally do, by slowing their metabolism, crucian carp can survive up to 140 days in anoxic ponds and lakes that have frozen over. (Goldfish can do it too, but can't survive early as long.) By staying in isolated ponds, they're safe from predators, and the low temperatures lower the metabolic rate.

From Hakon, Flickr
All animals store energy as glycogen, a highly-branched carbohydrate molecule that can be rapidly hydrolysed (broken down) into glucose for rapid release of energy by respiration. Crucian carp build up their stores of glycogen over summer, so come winter, there's enough fuel for the not-that-efficient anaerobic respiration. A lot of glycogen is stored in the brain, hence the history of surprised fish head dissectionists.

To keep functioning properly, crucian carp have to get rid of the products of anaerobic respiration, like lactate, which would otherwise build up. The enzyme alcohol dehydrogenase (ADH) is unique to crucian carp and goldfish, and it converts the waste products into ethanol, which readily diffuses through the carp's biological membranes, into the blood and out of the system through the gills.

Sources:
Science Direct
Wikipedia
New Scientist

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