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Winter Pond Fish Care

on December 15, 2020

New pond owners often ask about winter fish care during winter months, especially when extremely cold temperatures are predicted. 

Venturing outside on a cold winters day to find your pond frozen is always worrying, especially to the more inexperienced pond owner.  However, as long as the pond is not frozen to the bottom, and an air hole is provided on the pond’s surface, your fish will survive the cold spell.  With a deep enough pond (at least two feet deep) the fish will happily hibernate at the bottom, but they will still need oxygen.  A pond aerator or recirculating pump works a treat if you have turned off any waterfalls/pumps to avoid frost damage.

A pond cover may prevent snow and leaves falling in the water, but it actually will be detrimental to your pond life as it blocks sunlight.  This means your pond plants will suffer, and the quality of the water will be damaged.  A pond net is a good alternative as it will stop large debris from entering your pond, but still allow light through.  Should it snow, it’s important to clear the snow from the net as this can block light from entering the water.

If you don’t have one, a heron decoy or heron scarer can be a good investment in the winter.  Studies have shown that more herons enter the UK throughout winter months, so it is worth putting a preventative measure up to avoid your fish becoming food!

Winter fish care for ponds

What do I do with my pond fish in the winter

Pond fish become dormant and hibernate once the water temperature drops below 10c (50F).  At this point, you might want to stop feeding them, this is due to the enzymes needed for digestion in Koi fish is reduced, and so it takes much longer for the fish to metabolise the food and the food can just rot in the fish’s stomach.  When the temperature drops even further, fish will just not eat.  When feeding fish in cold (5-10c) temperatures, wheatgerm fish food is a good choice as it can be rapidly digested.

It is important to keep a gap in the surface, should it freeze.  This allows poisonous gases to escape as well as letting oxygen into the water.  A pond heater helps keep an area free of ice, rather than heating the whole pond and is a useful addition.

Frozen Pond Fish

What do pond fish eat in the winter

Pond fish such as goldfish and koi do not each much once the water temperature drops below 10c.  As their digestion slows, if they eat too much it risks rotting in the stomach before it can be metabolised, risking illness or death.  Feeding fast digesting food such as wheatgerm helps mitigate this risk, whilst still keeping your fish fed.

Once the water temperature drops lower than this or even freezes, your fish will go dormant and hibernate at the bottom of your pond.  They do not require food at this stage, only a hole in the ice to ensure that fresh oxygen can access the pond water.

When should I stop feeding my pond fish for winter

Feeding your pond fish should be dictated by water temperatures and fish activity.  Once the pond water drops below a certain temperature, your fish will require much less or zero food.  A good fish food to have during the cold winter months is Wheatgerm as it is quicker to digest.  However, once pond water gets really cold, your fish will not require food as they will be hibernating. 

Winter pond fish plant covered in snow

Will pond fish die if the pond freezes over

When the temperature drops low enough to freeze over a pond, it will form more of an ‘ice cap’ than freezing the pond solid, which is very rare.  This ice cap will cover the surface of your pond and will still allow some airflow, however it is greatly reduced.  Your fish is also using less oxygen, so in this state it can be left for a couple of days.  However, it is better practise to create a hole in the ice cap so it can release ammonia gases and exchange oxygen.  Try to do this by using boiling water or a pond heating unit rather than breaking a hole in the ice with a tool, as this can cause stress to your fish.  The reduction of oxygen can be further worsened with heavy snow, as this can cover the oxygen producing plants, so it is important to keep them clear of snow if possible.

In this ice cap state, your fish will fall dormant at the bottom of the pond where it is unfrozen.  But they will happy and healthy with plenty of sunlight and with you ensuring fresh air can reach the water.

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