Supporting your fish and pond throughout the winter

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With winter on its way there are certain steps fishkeepers need to take in order to ensure ponds and their fish are supported and in the best possible condition during the cold weather. To help you through this seasonal change, Dave Hulse Technical Consultant at Tetra shares his guidance and top tips when it comes to understanding how temperature changes affect your fish, the impact of lower temperatures on water and how to best protect your equipment.

With winter on its way there are certain steps fishkeepers need to take in order to ensure ponds and their fish are supported and in the best possible condition during the cold weather. To help you through this seasonal change, Dave Hulse Technical Consultant at Tetra shares his guidance and top tips when it comes to understanding how temperature changes affect your fish, the impact of lower temperatures on water and how to best protect your equipment.

Understanding how temperature changes affect your fish

The fish in your garden pond are ectothermic. This means their body temperature conforms to the environmental temperature and therefore will be equal to the temperature of the water around them.

As the water cools the fish will be much more sluggish and vulnerable to predation from herons, cats and mink, and cooler temperatures also mean the fish’s metabolic rate drops considerably. In fact, for every 10˚C drop in temperature the metabolic rate halves. This lower rate of metabolism means the fish need less energy and so they eat less. Also, their digestive tract is much less efficient, so they digest what they eat less promptly. Therefore, it is vital to feed your pond fish a diet that gives them energy but is easily digestible. Continuing with feeding standard pond feed which is less efficiently digested will result in excretion of undigested protein into the water and increased pollution. Alternatively, offering the fish no food at all over winter should never be considered as this will cause the fish to use stored energy reserves found in fats and muscle which will lead to them losing condition as well as making the transfer into spring much more of a challenge.

To support your fish, switch to wheatgerm foods such as Tetra’s Wheatgerm Sticks when water temperatures drop below 10°C, offering a small amount of food until the temperatures fall to where the fish naturally cease feeding. And remember to always remove any food uneaten after 20 minutes or so.

Supporting fish’s immune system

It is not only the digestive system of the fish that reduces in efficiency when water temperatures drop, but the immune system too. Research shows that it’s primarily the adaptive immune system that declines with temperature; this is the facet of immunity that is specific to particular pathogens. However, elements of the non-specific immune response, those cells and molecules that provide an ongoing vigilance and defense against incoming pathogens, are still moderately active. In fact, a group of white blood cells known as the phagocytes, whose role is to engulf and destroy incoming pathogens have been shown to be present in greater numbers and more active in the winter months. So, although many aspects of the immune system are temperature-dependent, some temperate fish have evolved measures to not leave themselves totally vulnerable to pathogen attack over winter.

Adding immunostimulant agents such as beta-glucans, an ingredient also found in Tetra Wheatgerm sticks, enhances the activity of these phagocytes and will further help the fish survive the winter period.

The impact of lower temperatures on pond water

As we move into winter, it’s important to understand that although the air temperature may fall well below 10˚C on a cold frosty morning, this isn’t necessarily true of the pond water. That’s because water is an excellent buffer to air temperature change, so though the daily temperatures may fluctuate considerably, the pond water temperature will slowly decline. This is due to the high specific heat capacity of water and it is vital in preventing exposure of the fish to large water temperature changes which would undoubtedly harm them. So, as the weather cools ensure you monitor your pond water temperature, rather than air temperature, to guide your switch to a wheatgerm based feed.

When temperatures really plummet, you may notice an ice sheet forming over the surface of the water. This can prevent oxygen from getting into the pond and stop carbon dioxide escaping, so it’s important to create a hole in the ice. This must be done carefully as breaking a hole with a hammer can shock fish. Instead, place a saucepan of boiling water and maintain the hole by using a floating pond heater.

Protecting your pond equipment

It is not just the nutrition of your fish that is important to consider over winter, we also need to think about the wider pond environment. It is vital that waterfalls, fountains, air pumps or any other aeration devices are switched off in winter and there are several key reasons for this. Firstly cold water can hold much more oxygen than warmer water, so we don’t need to aerate as much. This is because the fish’s requirement for oxygen is much less as the water is cooler in winter. Much more importantly though, aeration increases the contact between pond water and the icy cold winter air, which super chills the pond. This can cause the water temperature to plummet to a level where the fish suffer.

Switch off fountains and air pumps and ensure filter returns via waterfalls are diverted so that flow returns under the water surface causing minimal disturbance. Raising the pump 1-2 ft from the bottom of the pond encourages a layer of mildly warmer water to remain undisturbed where the fish can retreat. Gravity fed systems should also return under the water level of the pond. Try to reduce flow rates through the filter and perhaps feed the filter via a single bottom drain rather than multiple feeds. Any exposed pipework should be insulated with bubble-wrap or similar to help minimise chilling of the water and ultraviolet clarifiers should be taken indoors or covered as they are susceptible to frost damage.

Overall, winter is a time of minimal activity in the pond, but that doesn’t mean you don’t have a role. By taking care of your pond you’ll ensure that the transition from winter to spring is much easier and your fish are in a stronger position as they slowly become more active.

For more information about Tetra, visit www.tetra-fish.co.uk or join in the conversation with Tetra UK on Facebook.