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  • Sara Thompson

How do fish survive winter?

By Sara Thompson

Special to the Enterprise

Fish are cold-blooded animals, meaning they cannot regulate their own body temperature and require heat from their surroundings to be able to function and live. If fish need a warm environment, how then, can they survive in cold water during the wintertime?

Freshwater fish are in lakes and rivers at the end of the fall and are still there in the spring. Most freshwater fish have adapted and evolved to deal with the changing seasons and temperature. While the temperatures get colder at the surface of the water, it is actually slightly warmer closer to the bottom for the fish. The opposite is true during the summer when the surface is warmer than the bottom. During the fall the water temperature begins to even out and it goes through a turnover where the warm and cold levels reverse. During the winter, ice cover insulates the water a little, adding to the warmer depths. The water at the bottom would still be considered cold to most organisms, ranging around 350-500 F, but when the surface is freezing or below, that might feel comparatively warmer to a fish.

While the fish are gathering towards the bottom of the water, they also have the ability to slow down their metabolisms. Reduced activity reduces their need for food and oxygen. Plants in the water will still perform photosynthesis if light is able to penetrate the surface. However, as the ice and snowpack get thicker, this process can stop and potentially cause anoxic environments. Fish need to be aware of the oxygen levels of where they are and move to a new location if necessary. During the winter, fish not only use their gills to gather oxygen from the water but can also be absorbed from through their blood vessels, skin, and organs, some fish can also gulp air bubbles that form under the ice.

Slower metabolisms can help reduce the fish’s need for food but does not eliminate it. The underwater food web is still active during the winter, albeit a little sluggish. Fish will continue to search for food during the warmer parts of the day or lay and wait for something to swim by it. Ice fishermen have learned to use bright colored lures and long lines to attract fish at the bottom of lakes in winter.

The fish tank at Explorit is heated throughout the year so our fish are always active. Come visit Explorit during our public hours to check out the fish and living plants in our tank in the Animal Alcove. Explorit is open Fridays from 1-4pm and Saturday and Sundays from 10am-2pm.

Exploit's coming events:

• Thanksgiving Extended Public Hours: Monday-Wednesday, Nov. 21-23 10am-2pm; Friday, Nov. 25 10am-4pm.

• A Membership to Explorit grants the recipient free visits to Explorit’s regular public hours, discounts on events, summer camps and workshops, and gives you ASTC benefits to visit other museums throughout the world. To purchase or for more information visit or call Explorit at 530-756-0191.

• School Programs are available to schedule. We have educational programs that travel to schools and options for field trips at our facility. Please call 530-756-0191 for more information or to schedule.

• Now is a great time to donate and help Explorit continue to educate and inspire the scientists of tomorrow:

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