Koi are omnivorous, and will eat all kinds of things. Specialist koi food is a good idea, though, as it's carefully created to have the right nutritional balance for them. It also floats, so that the koi will come to the surface and you can watch them feeding.
Types of koi food
Koi food comes in two basic kinds – plant-protein and animal-protein. Plant protein is more easily digested by koi, so is a good choice for winter when their metabolisms are slower, and animal/fish protein for summer, when they're building up the reserves that will see them through the winter.
Koi food in Japan is often made from rice and seaweed, but you can also get koi food made from corn, beans, and all kinds of other things. The best option is probably protein from fish meal, but the important thing is it has the right balance of protein and other nutrients. For normal feeding, koi food should have about 32% protein. If you want your koi to grow quickly, then make sure their food contains about 40% high-quality protein.
Koi food also comes in different size of pellet. Choose pellet size according to the size of your koi, as small koi can't cope with big pellets.
Store your koi food in a cool, dark place, otherwise it may become rancid. If your koi food smells bad, throw it away.
Feeding koi fish
Koi are really clever, and after a while, your koi will actually come to recognise you, and swim straight over when they see you coming to feed them! You can train them to take food right out of your hand – having your fingers nibbled by koi is a fun experience, especially for kids. Do wash your hands afterwards, of course!
Koi will eat just about as much as you throw at them, but they only actually use a certain amount of it. Feeding them more than they need will increase their waste products, which will increase the nitrate and ammonia levels of your pond water, poisoning your fish. It will also encourage algae. So, it's important not to overfeed your koi.
How much should you feed koi? About 3% of their bodyweight is what they need to get by, when the water's warm – so about 30g for a 1kg fish. If you're keen to have them grow fast, then you can go up to double that amount – but not more than that. But watch out for signs of overfeeding, and cut back if necessary. You need a good filtration system to cope with high levels of feeding.
One way to keep your koi feeding to healthy levels is to only give them as much as they can eat in a few minutes, twice a day morning and night). Fish out any uneaten food with a net, and see how much there is. By seeing how much koi food is left uneaten, you can start to find the right amount of food for your koi.
Koi eat much less in the winter as their metabolism slows, so you'll need to adjust the amount of koi food you use throughout the year – more in summer, less in spring and autumn. Below 8 degrees C, koi don't need feeding at all, and it can actually be harmful to them. They also only grow when they're feeding, so they won't grow during the times when the pond is below 8 degrees.
Use a koi pond thermometer to keep an eye on the temperature (more about koi pond temperature) and adjust your feeding accordingly. In summer, you can increase feeding from two to three times a day. You may need to increase filtration as well, to cope with the extra waste the koi will generate.
