A look below the ice at fish behavior

Learn more about lake ecology with Michigan State University Extension’s Introduction to Lakes Online course.

Fish swimming in water.
Photo courtesy of Canva.com.

Winter is right around the corner and with that comes cozy blankets, hot chocolate and nestling inside the comforts of our home. Many animals act similarly during the winter, with some burrowing into nooks and crannies in the woods and others entering hibernation. Meanwhile, as the daylight hours dwindle, our lakes and rivers drop in temperature and begin to ice over. Many think that fish and other animals living under the ice would struggle to survive – but the reality is, many aquatic animals like fish have adapted to our cold Michigan winters in a variety of interesting ways.

How do fish survive Michigan’s harsh winters?

Similar to how our behavior changes in the winter, fish also behave differently with the climate around them. Fish are cold-blooded, meaning their temperature is regulated by outside influences such as temperature. They must modify their behavior to maintain their core temperature and survive. One way fish do this is by slowing down their metabolism and resting. Lake water next to the ice is colder and less dense than the water near the bottom of the lake. This phenomenon causes some species to school near the lake bottom to take advantage of the slightly warmer water. Some species also burrow into the lakebed for warmth.

Fish living in streams also seek out different types of habitats in the winter due to the unpredictable nature of ice jams. If a fish finds itself near an ice jam, it can lead to death or spending valuable energy to escape. Stable ice, rocky crevices, or plants, logs and dead trees are all different forms of shelter that are used by fish in the winter. Lake and stream restoration work typically includes the installation of logs since fish often use them as habitat all year long.

Do fish eat in the winter?

While many animals such as squirrels and woodchucks have the advantage of stockpiling food in the winter, fish have had to adapt in other ways to cold temperatures. Because there are limited amounts of food available in the winter, fish move slower and stop growing to use less energy. Some fish species also enter “diapause,” meaning a period with an extremely low heartrate. Fish will often slow down their metabolism to ensure they can survive on fewer calories. If feeding does occur, there are a variety of hatching insects to feed on as well as normal food web interactions of preying on smaller fish.

How can fish breathe underwater if it’s covered by ice?

One of the main limiting factors for winter survival for fish is obtaining enough oxygen to breathe. During the summer, plants produce high amounts of oxygen while undergoing photosynthesis. Simultaneously, diffusion from the atmosphere and wind turbulence and waves help mix oxygen into the lake. However, when there is ice cover it creates a barrier to the atmosphere and can even block out light for photosynthesis during heavy snowfall. This limits the amount of oxygen entering a lake. Since fish can slow their metabolism in the winter, they need less oxygen and are generally fine. In some cases, lakes can have a “winterkill” where the oxygen levels become too low for fish to survive. This is typically not an issue in lakes that do not have much plant and algae growth. However, in lakes with higher amounts of algae and plants, oxygen levels can get too low for fish to survive in the winter.

Wintery fish fact

Did you know there are some Antarctic fish that can create a special protein in their blood that essentially acts like antifreeze to prevent crystalized blood? This is how many fish in polar regions can survive such extreme temperatures and avoid becoming a “fish-sicle”!

How can you learn more about Michigan inland lakes?

Interested in learning more about your favorite lake and what goes on under the water’s surface? Connect with other lake homeowners and enthusiasts in the popular Michigan State University Extension Introduction to Lakes Online course. The course is designed for anyone interested in lakes, including lakefront property owners, local government officials, lake managers and educators. The course is six weeks long and covers lake ecology, watersheds, shorelines, water law, aquatic plant management and community involvement. Each topic includes pre-recorded video lectures, activities, learning resources and discussion forums. There are also three Ask-an-Expert webinars hosted by professionals from Michigan State University; the Michigan Department of Environment, Great Lakes, and Energy; and the Michigan Department of Natural Resources. Introduction to Lakes Online is offered once a year and kicks off in January. For more details visit the Introduction to Lakes course webpage.

A version of this article originally appeared in the November 2021 issue of the Lakefront Lifestyles Magazine.

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