What happens to fish when the lake or river freezes up?
An ice sheet forms on the water body, leaving below it a slightly warmer world, though with an icy ceiling.
When water freezes to form ice, only the uppermost layer freezes. Ice is lighter than water, and floats on it, like a toy floating in a tub of water. Ice is also an excellent “insulator” – it prevents heat from escaping out. So under the ice sheet, is a warmer world, at around 1 to 4 degrees Celsius. This is why Eskimos from Iceland and Greenland build igloos to live in. Even though it is built of ice, the inside of an igloo is warmer than outside.
Under the icy ceiling, fish can live quite happily, because they are ‘cold blooded’ – they can adjust their body temperature to the temperature of the surrounding water. We are warm blooded – we have to maintain our body temperatures in all situations. where life carries on as usual, even in peak winter. They also do the ‘usual tricks’ of storing fat in their bodies, like squirrels and birds.
Still, they do have to eat once in a while! Big fish eat smaller fish, so they don’t have much of a problem. Smaller fish eat insect larvae and small insects found in the muck at the bottom of ponds and rivers, and can get by until warm weather.