The problem with fish is their enormous capacity for tolerating bad practices. They can be fed the wrong food for a long time and survive it. But if you take a close look at your koi, you will notice clear differences in them, depending on which feed you use: their health, body shape, colouring, growth and activity - these are all factors where you can see visible differences.
Many pond owners are happy if their fish "like" to eat the food they offer. But what does "like" mean? Firstly, your fish don't really have a choice and secondly, they can get used to almost anything. It depends on how hungry they are - just like with us humans. When fish accept a NEW food, this unfortunately does not necessarily mean this is the best food for them. Children almost always prefer sweets to healthy vegetables. There are tropical freshwater fish that greedily devour red blood worms - and then die as a result! Fish do not always know what it’s best for them. But a serious feed producer does know, because in our culture more work has gone into carp research than any other fish. If you google carp or koi nutrition, you will get many times more hits than for neons, the best-known ornamental fish. Over the centuries, people have learned which "tweaks" they have to make to get the desired results in their carp. Obviously you no longer want your koi to reach their size to be ready for slaughter as quick as possible, the emphasis is now on a beautiful body shape, perfect colour separation and strong colours. And the "tweaks" for these factors are well known.
What food shape is best? Food sticks or food pearls are the most common. Both are produced in the same way, the difference being that a long food sausage is cut short (pearls) or left long (sticks) during production. Sticks usually have more air blown into them and are therefore lighter. When buying feed, please never compare by volume, but always by weight, because the weight and the composition of the raw materials determine the price - not the size of a big bag full of bulky food!
Speaking of bags: Please open the food bag only briefly to take out the food and then close it again carefully. Air and light can kill off the vitamins in the food! After about three months, an opened food bag should be used up. After that the vitamin content of the food drops very sharply until it’s not much better than edible paper.
The size of the food is really crucial for mouth-friendly intake. Small fish will have serious problems if they can only bite off or half swallow food that is too big. Large fish, on the other hand, will go crazy if they have to "slurp" food that is too small and it comes out of their gills again.
Floating or sinking? Koi are actually bottom feeders which use the barbels on their mouths to feel for their food in the bottom when they are burrowing. In a clean koi pond, this is a frustrating endeavour for the koi on the unlined bottom without a substrate. But they are very adaptable and quickly realise that the lumps on the surface of the water are edible or that the big shadow on the edge of the pond is not a heron but a food source they are willing to eat out of the hand of. Floating food in spring and summer is therefore no problem at all. In autumn and winter, however, the animals come to rest at the bottom of the pond and should also be given sinking food. As long as they are still actively swimming, they are consuming energy. If you do not feed your fish with external energy, they will be weakened during the cold seasons and susceptible to infections in spring (e.g. spring viraemia). A properly designed food with a protein/fat ratio of 3:1 in autumn and 2:1 in winter will prevent problems for the coming spring. The composition of the food has to be such that it is very easy to digest and yet has a high energy content. Salmon meal and fish oil fulfil this purpose in autumn to prepare for winter, whereas spirulina and corn build up strength in spring after the depriving winter.
The seasons mentioned are based on water temperatures: winter has water temperatures between 5 and 15 °C, spring has water temperatures between 10 and 20 °C, summer has water temperatures between 20 and 30 °C and autumn, like spring, has water temperatures between 10 and 20 °C. Depending on the water temperature, the appropriate protein/fat ratio should then be maintained. The highest protein-fat ratio should be fed in summer with 4:1.
The amount of food: The principle is that your fish should have eaten the food offered within a few minutes. Half an hour is not "a few minutes"! With prudent manufacturers you will find information on the amount of food on the packaging: 10 koi with a body length of 15-35 cm need e.g. 14-68 g/day, depending on the food type. JBL has a nice idea with a Misurino JBL ProPond that indicates the right amount on the cup depending on the food type.
Snacks: Proper treats ( PROPOND GOODY ) that will have the koi eating out of your hand. And that can be important! Get your koi used to hand feeding. This way you get very close to the koi and can recognise diseases more easily. If a koi has to be caught, it’s easier to do if you have their trust!
Koi nutrition is not rocket science, but it really is the cornerstone for beautiful and healthy koi. Take a little time when studying the packaging and compare! You now have the basics for assessing good food quality.
You can find more on nutrition here: Alimentazione dei pesci
You will find an outline of the different fish foods for pond fish here: Alimentazione