As omnivores, koi eat plants, usually duckweed and softer aquatic plants, and worms, which they will sometimes dig for using their jaws. Overfeeding koi is bad for their koi health both directly through being overfed and indirectly as both surplus food and excess wastage will pollute the water of the koi pond. Young koi eat noticeably much less than adult koi as their intestines have not developed to the significant length of that of an adult.
Normal practice is to feed koi twice per day, morning and evening, during the summer. A good method is to give the koi as much as they appear to want during three minutes of starting to feed. After the initial eagerness, their appetite will ease off, so the keeper can reduce wastage by this method. Commercial koi food, often in the form of pellets which come in various forms and different sizes related to the size of the koi fish being fed.
Live food can be stored in frozen form, which will have removed unwanted organisms, but can be expensive. Frozen koi food should be thawed out before feeding the fish. Changes to koi diet should be done gradually, over at least several days, by gradually mixing new food with the original food.
Koi Treats
Whilst it is important to control the koi diet, treats provide the opportunity to both balance and vary koi food. The most popular form of treat for koi is lettuce. Initially the koi should be fed on individual leaves. The koi's liking for lettuce will be demonstrated very quickly, and this will enable the keeper to put a whole lettuce on the surface of the koi pond; it will only be necessary to remove the remnants, which will be only the stalk, later!
Another treat to which koi are very partial is minced garlic, which can be added to other food for the koi fish. Other items can include:
- wheatbread and vegetables
- frog tadpoles
- aquatic worms, such as bloodworms
- earthworms
Koi do not have a digestive system that will cope with some items, for example:
- Large earthworms should be cut up before feeding.
- Even some mild forms of casings on food can be difficult, so peeling grapes is advisable.
- Oranges should be peeled and cut into small pieces but leaving the rind on then removing it from the pond surface later works well.
- It is also wise to ration fruit as it contains natural sugar, which in high amounts can be detrimental to koi health.
Seasonal Feeding
Koi's growth is usually rapid in summer and slow in winter. This creates the koi's rings of scales, which allow the age of the koi to be estimated in a similar way to the rings inside a tree stump. Koi will naturally eat more in the warmer weather, and colour-enhancing feeds, if used, are usually administered in the summer. This process is known in Japanese as "iroage". Iroage foods are often based on dried shrimps and a form of algae known as spirulina.
The koi appetite declines in the autumn, so food should be reduced. At this time, changing the balance in the diet from high protein to wheatgerm is also good practice. This should be reversed in spring, while gradually increasing the overall amount. If the koi pond is unheated, outdoor koi should not be fed in winter, as they will not normally eat at temperatures below forty-five degrees fahrenheit.
At temperatures below sixty degrees, koi will only need feeding once per day. If feeding at all in the winter, sinking food should be used. Koi will be largely inactive at this time and are unlikely to come to the koi pond surface. Their winter diet is often as little as 10% and certainly less than 20% of their summer intake. In spring, as the koi are starting to feed again, all parts of the diet should be easily digestible.
Hand Feeding Koi
The koi's gentle nature enables their keeper to train them to be hand-fed. Starting training as soon as fish are obtained is preferable but even koi that are used to their environment can be trained to overcome their instinctive fear as well. Whilst it will not happen immediately in most cases, training will be successful within a relatively short time. It can be accomplished using a simple procedure:
- Feeding koi always from the same position of the pond starts the recognition process.
- Slow and no sudden movements will reduce the risk of frightening the koi.
- By slowly putting a treat in one hand then putting it under the water, holding very still and letting the food fall into the water, the koi will begin to recognise a routine.
- After a few days, koi will come to the keeper's hand but in all probability will be reluctant for a while longer to take food directly from the hand. If the hand is withdrawn without feeding them, they will not starve in any case but will shortly come to accept that the hand holds the food and will start to feed from it.
- By repeating the practice, the process can then progress to feeding using fingers.
Feeding by hand also provides an opportunity to observe any change in the condition of the koi. If the koi pond is not overstocked, the poor appetite of an individual on more than one occasion whilst others are feeding well will alert the keeper of a potential health issue, as well as any visible signs on the fins and body.
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