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Understanding How Fish Survive Winter in Ponds

Having a pond with gorgeous fish in your garden or backyard adds to the charm and beauty of your outdoor space immensely. However, if you have just installed a pond and are about to experience your first winter, then you may be wondering, how do fish survive winter in ponds?

Winter can be quite a challenging time for most living organisms, including your pond fish, especially when your pond freezes over.

So, in this guide, we’ll discuss how do fish survive winter in ponds and a few tips and techniques of what you can do to help them survive the cold snap.

How Do Fish Survive Winter in Ponds in Nature?

Fish are cold-blooded creatures and in nature, they can live and survive in lakes, ponds, rivers and streams. Fish living in larger water bodies usually move to deeper or calmer waters. In nature, the fish adopt various ways by which they can survive the cold winter months naturally.

Typically, in deep freshwater lakes or ponds, the warm water settles at the hypolimnion or bottom because of its higher density and the cold water rises to the epilimnion or the surface, where it may freeze and this process is known as winter stratification and usually, hardy pond fish such as goldfish and koi assemble here to overwinter.

During the colder months, when the temperature falls, the metabolism of the fish also drops and to conserve energy and oxygen, the fish stop moving around.

Since these are cold-blooded creatures, fish cannot regulate their body temperature and enter short-term hibernation (or torpor) or they may go into full hibernation for the entire winter until the temperature of the water becomes optimal and their metabolism is restored.

To keep warm in winter, most types of pond fish burrow into the sediment at the bottom of the pond partially or fully to keep themselves warm and they become dormant.

Typically, the fish hunt for still water where there is no current because this tends to drain away their energy and warmth. They also reduce their feeding because of the slowed metabolism to reduce the use of oxygen and energy. The fish usually survive on algae growing in the water.

Typically, wild fish species like salmon, sunfish, trout, etc. are well adapted to very cold conditions and can survive in very cold water. Trout and salmon can in fact thrive quite well close to the surface of the water despite the very cold temperatures and they feed well all through the winter.

Author Note: Often, ornamental fish in home ponds may not be able to acclimatize to very cold climates and so, homeowners may have to adopt certain strategies and techniques to help the fish to survive the winter months.

Read on to know what you can do to help your fish survive the winter in your pond at home.

How Do Fish Survive Winter in Ponds at Home: Tips and Techniques

Goldfish under the ice

Clean the Pond before Winter

You should make sure to clean your pond and remove all the organic waste and debris like dead vegetation, leaves, fish waste, etc. before winter because these will decompose in the water, use up the oxygen and also introduce toxic gases into the water.

This can be a huge hazard in the winter because as it is, the oxygen reserves are quite low because of the ice and lack of oxygenating plants, the decomposing material only causes the precious oxygen to get depleted further.

So, it is recommended that before the winter sets in, you should clean your pond and remove all the leaves, debris and other organic matter from the bottom of the pond so that there is sufficient aeration and ventilation during the winter months.

Also, since the cleaning process will stir up the sediment, it is a good idea to change and replace half of the pond water with fresh water.

Use a Deicers or Surface Heaters

During the cold winter months, the top of the pond may freeze and it is vital to maintain a hole in the ice to allow the proper exchange of gases.

You can use a deicer, which is a dish-shaped device that is placed on the top of the ice. The deicer melts a hole in the ice and keeps it melted all through winter.

Some models of deicers can be placed under the surface of the water, which turns on and starts working automatically when the pond water starts to freeze. While this option is quite easy to use, it is quite expensive to run.

Use an Air Compressor

An air compressor or aerator is a highly efficient, yet cost-effective option that helps to maintain the water movement and increase the oxygen content in the water.

Author Note: The air compressor causes the existing ice to weaken, forming a hole or several holes or preventing the ice from forming fully, facilitating gas exchange.

While this method is quite cost effective, it may not be suitable for all fish species because many fish avoid moving water in the colder months.

The best way to use an air compressor is to make sure that the model you buy is not very powerful and does not disturb the water or the fish a lot.

Use an Inline Heater or Boiler

garden pond with goldfish

You can use a gas-powered boiler or an inline heater to prevent the pond water from freezing.

When the temperature of the water falls below a certain level, the heater or boiler switches on and passes the pond water via their heating chambers, which warm the water. The heated water is then pumped back into the pond.

However, an important thing to remember is if the water is a lot cooler than the desired temperature before you install an inline heater or boiler, then you should heat the water gradually, around 1 degree a day to prevent the fish from getting shocked.

Move Your Pond Fish Indoors

Some of the fish in the pond, especially the tropical varieties or if they are young or weak may not do very well in the pond during the winter.

It may be a better option to move these fish into an indoor aquarium or pond with regulated temperature and other conditions that will help them survive the winter better.

Typically, ornamental fish varieties such as black moors, orandas and plecos may have to be brought indoors during the winter.

Ensure Proper Feeding

Typically, the metabolism of the fish slows down naturally during the colder months and they don’t eat a lot.

Avoid over-feeding your fish because the fish will not eat the food and the excess food will simply float around in the water and break down and rot, reducing the water quality, as well as the oxygen levels in the water.

Top Tip: If the temperature of the water falls below 60°F, it is recommended to increase the carb content of the food, while reducing the protein content because the fish find it difficult to digest protein in colder weather.

Further, the fish excrete the excess food in the form of ammonia, which can be quite toxic to them and even fatal at levels as low as 1 ppm (parts per million).

And, if the water temperature falls to levels below 50°F, then it is advisable to avoid feeding the fish completely until spring. During this time, your fish will be able to survive by eating any plant matter, algae or insects in the water if required.

Increase the Depth of the Pond

The more the depth of the pond, the better the winter stratification, which means that your pond will probably not freeze right to the bottom and your fish will have sufficient space to hibernate in the winter and escape the cold.

If the winters in the area you live in are very harsh, then it is recommended that your pond has a minimum depth of at least 4 feet or more.

Avoid Removing the Ice and Snow

beautiful koi fish in pond in the garden

The layer of ice and snow on the pond can help to insulate your pond and protect it from harsh winds and temperature fluctuations, especially if you live in the northern region because the snow and ice layer can help to protect your fish.

However, you still must make 1-2 holes in the ice to facilitate the exchange of gases. In southern areas, as long as the temperature of the water is above 50°F, there is no need to overwinter your pond.


Which Fish Breeds Are Best for Winter Ponds?

In areas experiencing mild winters, you can fill your pond with any type of fish without any issues. However, if the area you live in experiences harsh cold and plenty of ice and snow, then there are fewer fish varieties that are suitable for your pond.

Some of the hardy fish varieties that are suitable for winter ponds include goldfish, koi, bluegills, archerfish, golden rainbow trout, fathead minnows, sterlets, rosy red minnows, and sticklebacks.

How Can You Ensure That Your Pond Fish Survive Winters?

The fish that will survive best in your pond in winter depends on several factors such as the severity of winters, size and condition of the pond and depth of the water in the pond.

The way that you winterize your pond and the steps you take to protect the fish from the weather can be vital in ensuring how well your fish will survive the harsh winter conditions.

It is important to remember that in the winter if your pond freezes completely right from the top to the bottom, no fish can survive this despite being hardy or how effectively you have winterized the pond.

Do Fish Fall Ill in the Winter Season?

Fish are susceptible to developing diseases during the cold season. However, they may not really fall ill because of the cold.

It may be because, by the end of the cold season, the fish tend to be weaker and their immune systems may be weakened because of the cold, which may make them easy targets for bacteria, viruses and other parasites.

Wrapping Up

So, we hope that after reading the article, you have all the information you need about how do fish survive winter in ponds. Pond fish are quite strong and resilient and they can survive in very low water temperatures as long as the pond does not freeze completely.

However, if the winter is long and harsh, even with proper preparations to protect your fish, you can expect some losses.

Nevertheless, by following the tips and techniques we have discussed in our article, your pond fish are sure to get back to their normal life and thrive well when spring arrives.

Happy Hunting!


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