The Different Ways that Fish Adapt to Frigid Water Temperatures
When Old Man Winter comes to the Great White North, most things slow down significantly, particularly those things outdoors. This can be seen most visibly along the many ponds and lakes in those areas of the country that regularly see sub-freezing temperatures. But don’t be fooled…though the lake may be still on the surface, there’s still activity below the ice. That’s one of the reasons why ice fishing is so popular on many northern lakes.
It begs the question, though—how do the fish survive when the lakes and ponds turn into a big sheet of ice? Let’s look at some of the reasons.
Most Lakes and Ponds Don’t Freeze Entirely
It would seem to make sense that water exposed to freezing temperatures would create a solid block of ice, but that’s not the case. Water tends to naturally expand when exposed to colder temperatures, breaking some of the bonds that cause it to be fluid. The physical properties of water cause it to be denser at 39 degrees than at freezing. The denser water sinks and the “airier” water rises and freezes, creating a layer of insulation for the deeper water. The greater density at lower temperatures also inhibits the natural expansion of the water, also preventing the water from freezing. As a general rule, marine life tends to migrate deeper in the water during the coldest parts of the year.
The Fish Change Their Metabolism in the Winter
It’s important to understand, first and foremost, that fish are cold-blooded creatures that can typically regulate their body temperature based on their environment. As a general rule, most fish can survive in water temperatures in the mid-40s but can be at risk when the water becomes any colder.
The fish also take specific measures to adapt to the colder temperatures. As a general rule, they will form schools in the deeper parts of a pond or lake and go into something akin to hibernation, where they remain stationary and at rest. Because they are not expending energy, their heart rates decline and their need for food and oxygen diminishes. Some species, such as catfish, will bury themselves in the muck at the bottom of a body of water, staying there until temperatures rise in the spring.
In addition, fish in some of the coldest parts of the planet (such as the Arctic and Antarctic Oceans) have, through evolution, developed a special type of protein that acts like antifreeze, preventing them from freezing even when the water temperature drops to below the freezing point of their blood.
