Date:
21 February, 2008
From:
Mallori
Question:
Why don't fish go into hypothermia in the winter?
Goofball Answer:
Mallori,
When it's winter time above the ice, it's actually summer below the ice. So the fish are actually basking in warm, watery glory right now. No wait. I think I'm confusing the ice with the equator. Folks vacationing on Argentina's beaches right now are basking in warm, watery glory. Sorry. I've been shoveling too much. My brain is cold.
And my frozen brain leads me to why fish don't get hypothermic in the winter...
Simply put, fish are ectothermic. Fish weren't ectothermic when your Mom and I went to school. They were simply cold blooded back then. But now they're ectothermic. Fish are so sophisticated now.
Anyway, ectotherms have simple metabolisms compared to homeothermic organisms—such as your Mom and me. With simpler chemical processes, ectotherms are able to maintain their metabolisms through a greater range of temperatures without succumbing to the elements. So whereas a few minutes under the ice would kill me, a fish is able to carry out its normal chemical processes in cold water.
There are some trade-offs for the cold fish, however. As their body temperatures drop, even though their chemical processes continue, they slow down. So the fish get lethargic, swimming and digesting food more slowly. To counteract this, fish will swim about in search of the warmest water they can find below the ice. The warm water makes their metabolisms run better.
Cheers...
~ topher
Notes on ice: Most substances expand when they warm up and shrink when they cool down. This concept is known as thermal expansion, except in one particular case, in which it is called "shrinkage". Anyway, water is unique. Water also shrinks when it cools down, but only to a point. Once water reaches 4 degrees celsius, it stops shrinking. After that, if it continues to cool down, water actually begins to expand, gaining size and becoming less dense as it turns into a solid. This is why ice floats—it's less dense than the cold water below it. So while the top of the river is all icy, the water below is most likely still flowing about, allowing the fish to swim around in search of water that's slightly warmer.
Notes on homeotherms: Homeothermic organisms, such as people, can only carry on their metabolic processes in a narrow range of temperatures. The advantage of this is that our metabolic processes run efficiently. So we don't have to slow down and eat our cheeseburgers slowly simply because it's a little cold outside. The disadvantage is that we must maintain our well-defined body temperatures to keep up this performance. When we're cold, we burn tremendous amounts of energy keeping warm, or we have to bundle up in down jackets, capilene underwear, and fleece socks. When we're hot, we have to sweat like mad to keep the evaporation going to cool ourselves down. And we have to take off the fleece socks.