How do Fish Survive in the Cold

Right now, here in Minnesota we are in a cold snap. Actually that may be an understatement. Right now, it is so cold that school has been cancelled 2 times in the past two weeks and two more days of school may be cancelled next week. The reason being...it is -30F with windchill! This pretty much never happens and could be a sign of the apocalypse. Also, because of this, many ice fishers are deciding to skip the fishing trip and move it to a later date. However, this got me thinking. While the ice fishers are on break, the fish are not. How are they surviving in this -30F weather?

I did some research on this topic and came up with some pretty interesting, and not at all obvious reasons. One of the first reasons that the fish survive in cold water is because of a property of solid water. Ice is less dense than liquid water, so when the water freezes it does not sink to the bottom, but instead floats to the top. This prevents the cold from freezing the whole lake.

Availability of oxygen is the second reason. As the water gets colder, it allows for more oxygen to be absorbed in water. Therefore more oxygen is available to the fish. However, not all of the water chills. Once a certain depth is achieved, the temperature of the water will increase and fish can take refuge in this warmer water. Often times, they will burrow in the mud and gravel, as well as in the surviving plants so that heat can be trapped and they are protected.

A third factor is the change in level of activity and food consumption. Certain fish species remain active throughout the winter and because of the increased oxygen, are able to go into certain waters they could not before. This gives more hunting grounds and prey. An example of some of the fish that fit this profile is lake trout and white fish. Other species become much slower and sluggish, and decrease their metabolism. This allows for them to use the extra oxygen for their most basic needs and decreases food consumption drastically. Some examples of these slower fish are Bullhead and Carp.

However, in certain situations, the temperatures are extreme, and the fish living in these environments need additional adaptations. The following was one of the coolest things I discovered. In the arctic, a lot of fish prefer to live near the ice because it provides food as well as protection from predators. However, this results in the danger that their blood will freeze. Therefore, to allay this problem, these fish produce antifreeze glycoproteins.  Their blood has chemicals, essentially that prevent it from freezing. I can't help but wonder if this is where we got out idea to put anti-freeze in fuel!

Fish are surprisingly interesting and extremely hardy in a lot of ways. When reading about some of these adaptations, I could not help but be impressed!