5 Tips for Raising Koi Fish

water depth for koi
water depth for koi should be a minimum of 3 feet

Raising koi fish is easy, but keeping them healthy needs a little extra care and attention.

Here are our top 5 tips for all koi owners.

1. Choose wisely

Raising koi fish that are healthy doesn’t start from the moment you add them into your pond. It starts right at the selection process. Whether you’re buying from a koi farm, a private dealer, or a pet shop, it’s important to choose fish that appear happy and healthy in their environment.

  • Don’t focus too much on the pattern or color of the fish as these are not always accurate indicators of good health.

Typically a more vibrant fish suggests deliberate breeding using the strongest gene pools, but in some cases the bright color could be due to the use of color enhancers in the koi’s food.


  • Look for fish that swim upright in the burst-and-coast style, rather than on their side, which can be a sign of disease.
  • Be wary of fish that seem to be trying to dislodge parasites. Similar to a dog trying to get rid of fleas.
  • Look for fish that are swimming calmly, rather than appearing excessively lethargic or racing around in a frantic panic.

Raising koi fish to be happy and healthy starts with a good, thorough selection process.

2. Create the ideal environment

There are lots of things to take into account when trying to create the perfect environment for koi.

  • Only purchase the number of koi that your pond can comfortably hold. Overcrowding can have a significant impact on the health and wellbeing of fish, with many suffering from stress when cramped, and an increased risk of disease resulting from overstocking.

As a general rule, you should allow at least 100 gallons of water per small koi, and 700 gallons for the largest koi. Remember that it’s not just other fish that can contribute to overcrowding. Too much vegetation can also be a major risk factor, so try to keep your sparse and dense vegetation to a 50/50 ratio.

  • Water depth should be a minimum of 3 feet, or 1 metre deep to allow the fish adequate space to grow. However many experts recommend a minimum depth of 5 or 6 feet simply because the added depth makes the pond look more pleasing to the eye. There’s no maximum depth for a koi pond, but digging a 20 foot hole may take some time!
  • Water temperature: Koi can live in water from around 1 degree celsius to around 32 degrees, but they’ll struggle in the more extreme temperatures. To raise healthy koi fish, keep the temperature between 15 and 25 degrees.

3. Feed them properly

  • During the warmer summer months, feed your koi roughly 3 times per day, offering food for up to 5 minutes assuming the fish are still happy to receive it (stop if the fish are no longer eating).
  • In the cooler months feeding your fish just once a day is enough to keep them satisfied.
  • If the temperature drops to below 7 degrees, stop feeding altogether. Your koi will enter hibernation mode and won’t require food until things start to warm up again.

One of the most important aspects of raising healthy koi fish is feeding them properly, knowing what to feed them, but also how often to feed them. Years ago koi were fed typical fish food almost exclusively in the form of flakes and pellets, but today many owners are feeding their fish all sorts of goodies, ranging from wholemeal bread and oranges to live food such as earthworms. We recommend switching up the type of food you offer regularly to avoid the fish becoming accustomed to just one type of food and refusing alternatives. With time, you may even find your koi are happy to eat from your hand!

Remember that koi can harbour cannibalistic tendencies, so don’t be surprised if they devour their own eggs. (However they should leave other fish alone).

4. Consider raising koi fish indoors if necessary

If you live in a cold area, you might add an air pump via a hole in the ice, to protect your koi during the winter. This ensures good aeration and water movement, and also allows waste gases to escape.

However keeping koi indoors is also very common when it gets a little chilly outside. If the temperature begins to drop below 10 degrees celsius, and you’re able to, think about bringing your fish indoors. A 12 inch koi will typically require around 10 gallons of water, so ensure you have an aquarium that can comfortably house your fish until the weather is better.

If you’re raising koi indoors, remember that a bit more effort is needed than if your fish are outdoors. The change in environment, and particularly in quality of water, may affect your koi. Keep an eye out for red ulcers or lesions on the skin – something that around 32 percent of indoor koi suffer with. Medicated foods and antibiotic water treatments can be very effective at treating ulcers.

5. Signs of koi diseases

As many koi are raised for profit, a large number are inbreed from the strongest gene pools. This means that a lot of koi suffer with weakened immune systems leaving them susceptible to disease. The risk of major disease can be reduced with good care.

The most common forms of koi disease are

  • stress
  • parasites

These are generally easy to treat but it’s important to know the symptoms.

What to look for

Koi that are stressed may jump from the pond in an effort to get more oxygen into their gills.

Fish affected by parasites may try to ‘itch’ themselves on objects, or display visible sores.

More serious diseases prominent among koi are the koi herpesvirus disease, and the carp edema virus which has an 80 to 100% mortality rate amongst young and immature koi.

As a koi owner, the best thing you can do is keep an eye out for signs of these diseases, which include lethargic swimming and sunken eyes. If you suspect disease, isolate the fish and talk with your local fish veterinarian.

Raising koi fish with care and attention is a fun and rewarding interest. If you look after them well you could end up with a koi that lives to 226 years old!