how do fish survive in the winter

You may be curious as to how do fish survive in the winter?

Don’t be concerned until you’ve learned the secrets of fish survival and their migration patterns during winter.

This article will explain everything, Keep reading! 

Fish have cold blood and can live in cold water. Fish slow their metabolism in the winter to conserve energy and live in lakes, unfrozen ponds, rivers, and streams.

At What Temperature Do Fish Survive?

Fish, unlike mammals, have cold blood and cannot control their body temperature.

The body temperature is influenced by its surroundings and heat, but heat cannot be created inside the body.

Fish exist in a wide range of environments and temperatures.

Arctic sea fish have a low body temperature, approaching below the freezing point of the water.

Other tropical fish found on coral reefs have a greater body temperature, averaging approximately 27 degrees Celsius.

How fish live with body temperatures that are the same as their surroundings has several important consequences for fish.

fish survive underwater

The temperature in various regions may change throughout the year.

Small freshwater fish can survive in almost freezing water in the winter but at greater temperatures in the summer.

Do Fish Get Cold?

Despite being cold-blooded, fish are quite sensitive to temperature variations in the water.

So much so that even a few degrees difference may occasionally be fatal.

Fish feel chilly, but the issue is what “cold” means.

Every fish species has a preferred temperature range. However, it differs greatly depending on their origin.

A tropical Lionfish could start shivering at 75°, but a Northern Pike would die of heatstroke at that temperature.

These individuals are quite tough; they’re made for different environments.

Note: Other threats that fish encounter in frigid waters include death. A regular fish's bodily fluid may harden if the surrounding water temperature falls below -5 °C.

How Do Fish Survive in the Winter?

how fish survive winter

Water is prone to freezing in the cold. The water starts to shrink as it cools. When the water hits four degrees Celsius, it begins to expand.

It will cease growing once it hits the freezing point. When the water on top condenses, its density decreases and the ice sinks to the bottom.

When the temperature falls below four degrees Celsius, the water becomes less dense and remains at the surface.

Ice develops at the surface, but the water underneath does not freeze.

For weeks, the temperature remains between zero and four degrees Celsius. 

Note: Despite ice on the surface of the water, heat travels considerably faster in water than in air. 

That’s why the fish thrive in the unfrozen water below. Fish don’t have any means of warming up.

However, Fish have evolved a few tactics to help them survive the long winter as follows:

1. They Migrate

Many fish, particularly saltwater ones, migrate. Where do fish go in the winter?

school of fish migrating

Some travel the globe, while others sail up and down the coast in search of their ideal bathing conditions. Despite that many fish migrate for several reasons. 

Most follow food or migrate to their spawning sites during particular periods of the year.

Temperature, however, has a significant impact on each of these. That’s why you never know when the fish will appear each year. It all depends on the weather.

2. They Enter Torpor

Migrating is great, but it is not always a choice. Some fish have nowhere to go, while others are too slow or weak to make the trek.

Instead, they must endure while the lake freezes above them or winter storms churn up icy water from below.

What is the simplest approach to do this? Go to sleep.

Fish do not hibernate, at least not in the traditional sense of the term. They instead enter a condition known as “torpor.”

fish torpor stage

This is similar to a profound slumber in which their bodies slow down, and they quit actively eating.

To be warm, some individuals go so far as to bury themselves in mud. If they sense danger or an easy food source, they may still awaken.

3. They Go on a Diving Expedition 

At first glance, there seems to be no trace of trout or roache.

However, the thermometer reads three degrees, indicating that it is significantly warmer beneath the ice than above. That implies that fish must be able to survive down here. 

This is due to a unique property of water: H2O’s elasticity. When the temperature drops below freezing, water contracts first, then expands as it begins to freeze.

Ice floats because it is lighter than water. This means that the lake’s surface is the first to freeze.

fish dive deeper

The deeper the water, the warmer it is for the fish:

Fish may find warmer water by swimming deeper and deeper. The water grows denser as you move deeper.

The temperature rises as the density of the water increases. Lake Lunz’s water temperature stays constant at four degrees Celsius, even at its lowest point. 

A lake more than one meter deep will never totally freeze, which means there will be plenty of room for animal and plant life to survive the winter.

Furthermore, the thick water in the lake’s deeper regions has a substantially greater oxygen concentration. This helps fish and other forms of life to survive until April.

4. They Innovate

Some fish are just used to the cold and can survive even in the dead of winter.

Arctic Char, a subzero specialist, thrives in near-freezing conditions. In reality, their bodies have been carefully evolved to avoid freezing.

For Instance, the true piscatorial forefathers, such as Bluefin Tuna.

They have the ability to reheat their blood, allowing them to hunt in cooler waters by keeping their eyes open and muscles powerful.

bluefin tuna

But how do they innovate? 

There are three major ways that fish undertake to adapt to cold temperatures:

They Contain Alternative Enzymes:

Most fish have alternative enzymes.

Enzymes are proteins that catalyze metabolic processes; nevertheless, the effectiveness of enzymes is temperature sensitive; enzymes work best at ideal temperatures. 

Some fishes have developed alternate enzyme systems called isozymes to execute the same job at various ideal temperatures to enhance their effectiveness throughout a wide temperature range. 

Other fishes use allozymes, which are various versions of the same enzyme regulated by different alleles and enable reactions to occur at different temperatures.

Note: Opah is the only fish becoming the world's first warm-blooded fish. 

Some Fish Retain More Ions:

fish retain ions

Other creatures outperformed the super-cold salty water. To maintain osmotic equilibrium, marine fish must continually export ions.

Retaining more ions, on the other hand, may enhance a fish’s freezing point and survival in subzero conditions.

However, some fish cannot tolerate the cold.

Threadfin Shad, in particular, are prone to massive winter die-offs, making them a key source of winter feed for many predators. 

Extreme temperature fluctuations often cause large-scale winter fish die-offs. In 2011, 100,000 drums perished in the Arkansas River when a freezing front swept through after many warm weeks.

Note: Many ponds and small lakes are experiencing winterkill massive fish die-offs caused by ice that hinders oxygen exchange rather than cold.

Some Have Antifreeze proteins: 

High salt concentrations in polar marine systems lower the freezing point of water to roughly -2°, which is colder than the freezing point of most species’ body fluids. 

herring underwater

Several species (notably the Notothenoidei, sea ravens, cods, and certain herrings) contain antifreeze proteins called glycoproteins that prevent blood from crystallizing in these environments.

They can live in the harsh, ice-covered arctic areas because of this.

They Slow Down Their Metabolism:

Although they can survive in various temperatures, cold weather affects their metabolism.

Small freshwater fish decrease their metabolism during the colder winter months, not growing, hardly moving, not eating, and breathing slower than normal.

Note: Prey fish hide and feed on plants during the winter when their body processes slow down. Predator fish will swim by these locations in search of a quick meal.

5. By Obtaining Food

Most fish survive the winter by searching for food.

Some species, such as crappies, perch, bluegills, and trout, can raise their body temperatures even in cold water, but they must eat enough. 

trout in lake

Like bears, carp, catfish, and bass will eat heavily in the months leading up to hibernation in order to store enough fat to last over the cold season.

Fish like crappies, perch, pumpkin seeds, and bluegills will scrounge around in the muck along the water’s edge in search of simple prey like aquatic insect larvae.

Northern pike and bluegill frequently lose weight in the winter because they can’t find enough food to compensate for the calories they burn to survive.

Note: Life in the freezing lakes in winter is quite similar to summer life, albeit slower and with less vegetation.

Final Verdict

How do fish survive in the winter?

Fish have cold blood and can live in cold water. Fish slow their metabolism in the winter to save energy and dwell in unfrozen lakes, ponds, streams, and rivers. 

Despite having these abilities, they may also go to the bottom of a lake where the temperature remains steady, then they enter torpor.

Thanks for reading!

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