Seasonal feeding for koi: nonsense or really important?

Feeding our fish often requires little more than common sense: only as much as the animals can eat in a few minutes, lots of variety, the food shouldn’t be older than 3 months. But it gets trickier when it comes to seasonal feeding. However anyone, whether experts or not, can expect the following from their fish food:


It needs to be easily digestible in winter, which mainly means it has to be very quickly digestible in low temperatures. If it isn’t it could lead to putrefaction processes in the digestive tract of the fish –and you wouldn’t wish this on anybody! Winter is a difficult season since the animals normally rest and no longer require any food. But winter rarely starts in one blow – it usually sets in gradually. The temperatures drop and the fish move less. They are, however, still active and this activity means calorie consumption. If we abruptly stop supplying them with energy it’s like when a human fasts. When the calorie intake lies under the calorie consumption, we lose weight. But we DON’T want this to happen to our koi! There are even foods which are so badly mixed that the energy consumption, which is necessary for the food conversion, is higher than the energy supply of the food itself! The koi are starving even though they are being fed! This extreme case shows very clearly how important it is to study the subject of nutrition (I mean fish nutrition ). When the temperature drops below 5-7 °C you’ll see that the fish have ceased to be active and their feeding needs to be completely discontinued. But when the koi are active (still or again) between 5 and 15 °C, you need to feed. But by all means with the right “winter food”!


In spring, with water temperatures between 10 and 20 °C, the animals often are weakened by the strains of winter and health problems can arise. A lot of owners are very familiar with such illnesses as spring viraemia. This is aggravated by the fact that the fluctuating water temperatures require enormous energy reserves on the part of the fish as they become more and more active. The floating food needs to feed the animals up after the winter and quickly supply them with energy. The correct protein/fat ratio of the food is 3:1.


In summer our common sense tells us: in high temperatures we need a lighter diet. It’s the same with the koi. A higher protein content (28%) and a lower fat content (7%) are advisable because the oxygen content of the water drops with higher water temperatures to its lowest values. The ideal protein/fat ratio is 4:1.


In autumn the water temperatures are the same as in spring, but the food requirements vary. The food needs to sink so that the koi don’t need to exert themselves unnecessarily, as they are beginning their period of rest at the bottom of the pond. To make the animals fit (fat) for the coming winter, the fat content is raised e.g. with salmon oil (10%). The protein/fat ration needs to be 3:1, as in spring, but with a higher protein and fat content!

Protein/Fat Ratio

The protein/fat ratio mentioned above is a really important value in koi nutrition. No fish has been so well researched through the centuries as the carp! And our koi are carp too, even though they are very colourful ones! But we need to be very careful how we apply the research results, because what is good for well-fed, cultivated carp may be undesirable for our koi. However research has not only been done into what makes carp stout and fat but also the opposite: when do carp start to develop problems and which nutrition has which effects? As a result we don’t need any guesswork. Skilled biologists, specialised in fish physiology, can select the appropriate information and know what’s best for your koi. JBL has collocated this information in a NEO index and based its feed composition on it. Scientists have agreed that in winter koi need food with a protein/fat ratio of 2:1, in spring and autumn 3:1 and in summer 4:1. Only with function foods for a special purpose (colour, growth, fitness) can the protein/fat ratio increase up to 6:1, as with the growth food for small koi. Don’t forget to check whether you need each ingredient; for instance spirulina can be useful in spring, but needs to be replaced by rich fish oil in autumn food. Every koi enthusiast needs to examine the composition of the food discerningly: the list of ingredients is always arranged in descending order. The raw ingredients mentioned first are used in the highest proportion. If, for example, fish is mentioned in the last position, all the ingredients listed before the fish are used in a higher proportion.

The Situation in Japan

It’s also interesting, of course, to look at Japan, where koi are bred in three regions: in the north of Niigata Prefecture, in centrally located Hiroshima and in the south where the well-known koi farm belonging to the Ogata family is situated. Shortly before the winter, usually in the middle/at the end of October, the koi are fished from the natural ponds. They are placed in sales tanks and dealers from all over the world arrive to personally select koi for their customers.

If these koi didn’t originate from a Japanese natural pond but from a German one, you might at first think they were too fat or even suffering from malnutrition-based dropsy! The koi have such an amazingly huge body shape! And these fish weren’t given any additional food during the summer! The micro fauna in these “mud ponds” are simply so extensive! The Japanese only give supplementary feeds in smaller natural ponds. There are no plants in these ponds and there is no algae to be found. Once they have been moved to their winter quarters the koi are not fed again before they are sold, although the water temperatures are between 11 and 22 °C. This, of course, is because the Japanese want to ship them with an empty digestive tract. Any unsold juvenile koi and koi carp with lots of potential (tategoi) are fed until they are returned to the natural ponds in spring.

And, by the way: The temperatures in northern Japan can drop as low as they do here! Whereas we may see several meters of snow next to each other, in Niigata they really lie on top of each other and transform the landscape into a winter fairy tale! That’s why the Japanese have known for generations that each season needs its own food.

© 10.10.2017
Heiko Blessin
Heiko Blessin
JBL GmbH & Co. KG

Tauchen, Fotografie, Aquaristik, Haie, Motorrad