Are Cold-Blooded Animals Cold? No, But Some Fish Have Anti-Freeze.

When I think of something that is “cold-blooded,” I think of a slimy reptile that is cool to the touch. You know what I mean, the animals that make little girls make a face and say “eew.”

Yes, some of these animals may be gross, but just because they’re cold blooded doesn’t always mean they’re cold.

It’s what’s on the inside that counts

In biology, we don’t call animals warm-blooded or cold-blooded. This name is a bit of a misnomer. The terms to use are endothermic and ectothermic. As it turns out, cold-blooded animals aren’t always cold, they just don’t make their own heat (for the most part).  Endotherms (warm-blooded animals, like us) can make our own heat. In fact, the word endotherm means “inside heat.” This means that if you stick us in a cold lake, our bodies will try to generate more heat to help regulate our internal temperature. We will actively try to bring our internal body temperature back to the normal, or homeostasis.

The environment can change the temperature of ectotherms

Ectotherms (cold-bloded animals), on the other hand, don’t actively regulate their internal body temperature. When you put them in the cold, their entire body cools down; along with its metabolism. If you put a snake in cold water, all of its body’s functions will slow down. This is why they like to bask in the sun after a big meal: it helps them digest.

What about fish? They live in very cold water.

Then, there are the fish (like the sea-raven depicted below) that live in icy-cold water. If they don’t regulate their own body temperature, aren’t their bodies the same temperature of the freezing water? Why aren’t they icicles too?

These fish are able to survive in the cold because they produce antifreeze for their blood. These chemicals, called antifreeze glycoproteins are produced in the pancreas of the fish. It’s similar to putting salt on the road to keep the roads from getting icy.

So, the next time you jump into a freezing lake, be thankful for the fact that you can warm yourself back up.

( fish photo credit stan_shebs; lizard photo credit: Aaron T. Goodman; cold swimmers photo credit: Ryan Forsythe)