Why Don’t Fish Freeze?
Although humans would never be able to withstand a long period of time in cold water (remember the Titanic?), many freshwater fish survive because of special adaptations that help with internal thermal regulation. Fish, in contrast to warm-blooded mammals and birds which maintain a constant internal body temperature, are cold-blooded animals. Their internal body temperature equals that of the environment around them. Freshwater fish avoid freezing because they are hyperosmotic, meaning they have a higher internal concentration of salts than that of their surrounding freshwater environment. This is important because it takes heavier or more concentrated liquids a longer time to freeze than less concentrated, just as it takes saltwater longer to freeze than freshwater. To avoid getting too cold, fish use either behavioral habits to move from one water mass or area to another in search of warmer water, or physiological means to keep at the proper temperature. In the wintertime you may hav
