Koi Health

General Health

There is no one secret to having healthy koi, but a good knowledge of several key factors can make it all that much easier. Unlike our other household pets, fish inhabit a world that is very different from ours. Because they live in a liquid rather than in air, most of their basic needs have to come from the water. It is often said that we don't keep fish, we keep water. To get the maximum pleasure from your koi you should be aware of these main factors of koi health;

Water Quality
It cannot be stressed enough that the single most important factor in the successful keeping of koi is the quality of the water. Poor quality water will almost invariably lead to trouble with the fish. Their general health and therefore resistance to diseases will drop dramatically, as will their growth rate and colour.
The water quality is affected by the other topics covered here as well as the water chemistry, which is invisible to us and requires the water to be tested to get the results. While water chemistry is quite involved it is essential for the health of your fish.

Stocking Rates
The amount of fish that can be kept depends on a few things but mainly, the volume of water your pond holds and the type and amount of filtration you can provide. Remember that fish grow for several years before reaching their maximum size of between 50-90cm and the amount of fish you have now may mean you will be overstocked in just 1 - 2 years of growth. A fish can weight just 115g at 20cm long, but at 40cm long, they have increased in mass by 8 times to just under 1kg. This requires 8 times more filtration than a fish half that length. While the idea to put just one more fish in your pond might seem to have little consequence, in a short period of time, gone unchecked your fish load could be greatly outweighing the filters ability to keep the water quality high.

The filtration of your pond can be done in many different ways and you can see our filtration page for more info. The filter provides a place where solid matter can be removed from the water to keep the water free of debris but more importantly is the main home of bacteria which are able to break down the waste product from the fish, which is toxic to a form which is much less toxic, which is then removed by water changes or through aquatic plants which use it as food. The filter must be of an appropriate size to be able to handle the volume of water your pond holds, otherwise the toxic waste will build up and poison the fish.

The right type of food is great for the development of your koi, but too much or the wrong type can pollute the water causing multiple problems for your koi's health. Only feed an amount that they can consume in 5 minutes and remove any excess, otherwise this will foul the water. During warmer weather koi will be able to eat more often, up to 5 times a day and during colder weather the amount of food should be reduced, to a point where in the middle of winter you can feed only once every second day. Healthy koi are able to go without eating for a month, as in Japan they can't be fed when the pond freezes over. Do not feed your koi if the water temperature is under 10C or over 30C.

Like all living things, koi still need to breath oxygen. Oxygen is not very soluble in water at the best of times and is greatly affected by temperature. There are a few ways to increase oxygen in your pond to ensure it is available for your koi. Water movement in contact with the atmosphere can be achieved with waterfalls, spillways and fountains. Otherwise you can force air into the water with an airpump through an airstone which allows the oxygen to be dissolved. You can never have too much oxygen so it is always best to provide as much as possible for times when your koi need it most.

Diseases & Illness
Unfortunately you may experience a fish which doesn't look right, or is acting strangely. The early detection of problems depends on careful observation and can be the difference between a full recovery or not. While quarantining any new fish is the best practice to stop the spread of any disease or parasite, your pond will always carry some form of bug which your fish will have a resilience against and only when their immune system is low might they be susceptible to a disease or illness. While some things can be easily treated others may require more extensive medication or even surgery.

By knowing how the above items play an important role in your koi's health you will be able to maintain a healthy pond which should help prevent any health problems. After having you koi for sometime you will know if something is not right. Here are good signs of healthy fish:

  • Spread evenly all over the pond, or schooling and swimming to all parts
  • Swimming strongly in upright position
  • Using their pectoral fins freely
  • Alert and interested to see you
  • Looking for food and eating eagerly
  • Gills opening and closing slowly
  • Colour is nice and bright
  • The eye is bright
  • The body is well rounded and fins in good condition

It would be impossible to write a comprehensive article on all koi health problems and how to fix them, so it is much better to prevent them from occurring. If you do have trouble, please contact the club or come to the next meeting to ask for help.

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