On Thursday I posted about the fate of the goldfish frozen in the pond next door. I thought they were goners. But, good news! Now that the ice has melted, the familiar orange bodies are darting around in the water again.
Miracle? Cryogenics?
No- when I stuck my head way over the fence to get a good look, I saw that a small section of the ceramic water container goes deep underground. Warm water is actually more dense than cold water, so the warmest water (and the fish) head as low as they can go.
Goldfish hibernate in the winter- lowering their metabolic rate and basically chilling out until the warm weather comes again. Wikipedia's article on goldfish in ponds says that as long as the entire pond isn't frozen (as I feared it had), the goldfish survive unharmed. In fact, goldfish are one of the few species known to survive anoxia, or the absence of oxygen. They survive by lowering their metabolic rate. As with our cryogenic frog friends, regulation of glucose plays a major role during anoxia and reoxygenation (waking up from anoxia).
Ironically the organs undergo the worst stress not during anoxia, but during the period of reoxygenation. The liver suffers the most, but the brain and kidneys are also affected. Goldlfish (and our friends the wood frogs) rely on the elevated presence of antioxidants in their body chemistry to ease the strain of warming up back to life again. (Source: Oxidative stress and antioxidant defenses in goldfish Carassius auratus during anoxia and reoxygenation).
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