Fish in the winter

Several species of fish can remain in your garden pond over winter without issue – subject to their habitat fulfilling a few basic conditions. Also discover whether you should feed your pond fish over winter or whether they go into hibernation.

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Fish are cold-blooded animals. This means that the outside temperature determines their internal temperature – and therefore their level of activity. As the water becomes colder, the animals’ metabolism slows down. They use less energy and can survive by drawing on their fat reserves. You could say that fish have a kind of winter dormant period or quasi go into hibernation until the water warms up and food stocks increase again in spring.
Feeding pond fish
Regardless of the above, it is still important to ensure that your fish have plenty of reserves to keep them going. You should therefore give your fish some reserves to eat in early autumn. Special transitional food is available for the time when the days start to get colder. This carefully prepares the fish for the winter by being easily digestible thanks to a high level of fibre but also strengthening them.
Pond heating

When winter temperatures really start to fall, shallow garden ponds can freeze completely. This is life-threatening for the fish. If your pond is not deep enough for at least some areas to remain unfrozen, you therefore have two options. Firstly, you can move your fish into your home over winter, for example, by placing them in a tank. Secondly, you can go with some pond owners’ preferred option of using a ‘pond heater’. In choosing the latter, however, note that such heaters use a great deal of electricity. 

For smaller ponds, electric flow heaters are sometimes even used as they can be easily retrofitted. However, all they really do is keep the pond free from frost. To do this, it normally suffices to set the temperature to approx. 4 to 6°C – the temperatures at which fish would survive over winter in the wild. To find the best pond heater for your pond, we recommend consulting a specialist.

Keep an eye on the water-quality parameters
For your fish to safely go into hibernation, you should keep a close eye on your water-quality parameters in autumn. You can check if these are as they should be using test strips. These measure the ph level, the carbonate and overall hardness, the nitrite and nitrate levels and the chlorine level of the garden pond water. This enables you to take any necessary action in plenty of time before a layer of ice covers the pond.
Use ice preventers to enable gas exchange

It is important for your fish that the gas exchange between the water and the air continues even in winter so that any fermentation gases can escape, for example. If the surface of the pond is covered in a thick layer of ice, it is very difficult for such an exchange to take place. 

Experienced garden pond owners resolve this problem by using an ‘ice preventer’. This is usually a polystyrene ring with a diameter of about 60 centimetres and several chambers filled with sand or water to weigh down the device. The aim is for the ice preventer to protrude just a few centimetres above the surface of the water. The structure is protected by a lid.

Hot water as an emergency measure
Leave your garden pond in peace! However, if the surface of the water does ever completely freeze, do not grab your hammer and chisel to hack a hole in the ice. The pressure waves that this causes can disturb your fish and even damage their health. Instead, carefully pour a pan of hot water onto the edge of the pond to create a small, ice-free area – and enable gas exchange. If you want to keep the hole open, you can hang the air stone that goes with the air pump through it.
AUTHOR: Tetra GmbH
DATE: 28.11.2016
SOURCE: Gartenteiche (Garden Ponds); Katrin and Frank Hecker, Gräfe und Unzer Verlag, 2013