Sad frog stories – updated

goldfish

Goldfish are amongst the most resistant of all animals to lack of oxygen when the water is cold; more resilient than frogs

From Louise who wrote on Saturday with another sad frog story:

I have a small/medium size pond and have lost nearly all my large frogs. They appeared to have come up to the surface for air, but because the pond was frozen for such a long period of time (over a week) they either froze or suffocated to death – poor things.

I have a number of goldfish that seem to be OK. I just wonder why the frogs woke up and came to the surface in the first place – when they should have been hibernating.

I am just hoping that the younger/smaller frogs have survived and are still at the bottom of the pond in the mud.’

So, why did the frogs come to the surface, and how did the goldfish survive? 

We know from careful studies of what frogs do in winter that they’re not completely tucked up at the bottom of the pond, waiting for the warmer weather. In fact they can move about, keeping themselves in the place that’s just right: with enough oxygen but so warm so they use up all their energy reserves, and not too cold so they freeze solid.

The problem is that near the bottom of the pond, though its the best place for getting the right temperature because it’s where the water’s warmest, its also the place where oxygen is likely to run out first because the mud at the bottom uses up oxygen.  

So it’s possible in this case that at the bottom of the pond the frogs ran out of oxygen – and when this happened they went looking for oxygenated water but couldn’t find it. And because frogs can’t survive more than four or five days without oxygen, at most, the cold snap was simply too long for them.

What about the goldfish? How did they survive? Well, Goldfish are pretty remarkable when it comes to lack of oxygen. They are some of the most resistant of all higher animals to managing without it. They can survive days or weeks without oxygen – indeed, a very close relative of the Goldfish, the Crucian Carp, can survive several months without oxygen.

So this probably explains why the frogs succumbed but the goldfish didn’t.

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