How Cold Water Affects Fish Behavior

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By Ty Moos, SDGFP Resource Biologist

All local fish species are poikilothermic ectotherms, a fancy scientific term describing cold-blooded animals with body temperatures that change with the environmental temperature.

When winter is on its way, many ectotherms hide and hibernate. For example, snakes find protected cavities to wait out winter, and aquatic turtles burrow into mud on lake or pond bottoms where they remain, holding their breath, all winter. In fact, painted turtles have been known to hold their breath for up to 180 days at near freezing temperatures.

Thankfully, many ectotherms do not hibernate. After all, it would be a long, cold, boring winter for ice anglers if yellow perch hibernated. But that begs the question, how does cold water affect cold-blooded fish?

Not all fish can survive a South Dakota winter. For example, most fish species commonly found in pet-store aquariums originate from tropical climates and would stand no chance of surviving under the ice. Tropical species are adapted to life in a consistently warm environment, and the Dakotas are anything but consistently warm.

On the other hand, fish species in the Dakotas vary in their adaptation to prolonged periods of near-freezing water. Some species thrive, while others only maintain throughout the ice-fishing season.

The reason for this is due to their metabolic rate, or the amount of energy required to maintain body functions. Fish adapted to cold water can maintain higher metabolic rates, allowing them to be more active.

One indication of a species’ temperature tolerance is its preferred spawning temperature. The colder the water when a fish spawns, the better adapted it is to cold water.

Fish classified as cold-water species are those that thrive under the ice. Cold-water species are usually active in winter and are primary targets for ice anglers. In northeast South Dakota we have a few true cold-water fish species, but none are native.

Rainbow trout are a cold-water species, which is why the South Dakota Game, Fish and Parks Department stocks them in some small urban fisheries or in the Missouri River in early spring and fall when water temperatures are cold. They cannot tolerate the heat in the summer months.

Northern pike are the closest thing we have to a native cold-water species in northeast South Dakota, although their tolerance to cold varies with size. Small pike do well in warm water, but as they grow their preferences change. Large pike seek out colder water and are less tolerant of warm water.

If you fish the Missouri River reservoirs you are likely familiar with burbot, which are sometimes called eel pout or ling. They are a supreme cold-water fish in that their metabolism is at its peak in very cold water. In fact, they even spawn in the middle of winter under the ice.

The most popular fish species among ice anglers in the Dakotas are classified as cool-water species. Northern pike, walleye and yellow perch can be grouped into this category. The native range of these species is primarily confined to the middle latitudes of North America. The popularity of these species with ice anglers is a reflection of their qualities as table fare and willingness to bite a lure or bait.

Pike spawn at water temperatures ranging from 40-50 degrees, while walleye and perch prefer spawning in water temperatures between 45-55 degrees.

The final classification is warm-water fish. The most popular of these include largemouth bass, white bass, bluegill and crappie. We are near the northern edge of their ranges, but the northern strains of these species are well adapted to our winters.

Bass species present in our lakes are not typically active during winter, but they are opportunistic feeders, which helps them get through the long ice season.

Bluegill and crappie are more active than bass, and they can go on an impressive bite even during winter. In our area, these species typically spawn at water temperatures of 55 degrees or more.

So, when you’re out ice fishing and the bite is slow, it may be worth your time to try and catch the most cold-adapted species in the lake.

— By Ty Moos, SDGFP Resource Biologist