Koi Food. Feeding for health.

The two most widely debated topics amongst koi keepers are nutrition and filtration.

This is very understandable when these two areas of the hobby are likely to have the greatest combined impact on koi health. As filtration is a very ‘hands-on’ and practical aspect of koi keeping, the science and principles involved are well understood and widely practiced. Koi nutrition however, is completely different.

Our understanding and appreciation of koi foods is limited, being at the mercy of koi food manufacturers that present us with long lists of ingredients and claims about their products. As we are not able to test or in extreme cases interpret the science we are rarely in a position to question such claims.

Consequently, myths abound in the world of koi foods and as our general understanding compared to that of filtration is quite limited we cannot fully appreciate the what, why, how and when of koi nutrition. That is, until now.

This is the first in a series of 6 articles on koi nutrition, looking at how koi foods achieve what they claim, (in delivering health, growth and colour), how they can interact with our ponds to cause other changes and how recent innovations may soon lead to a new generation of koi foods.

Feeding for health.

As a nation, we are gluttons of the western diet, and top the obesity rates of Europe. Equally, our level of education about our health and environment, has never been greater. We know what is good and bad for us, and yet we continue to choose the non-balanced route; a recipe for disaster and certain ill-health.

Our first consideration for our koi is that unlike us, they do receive a well-balanced and complete diet. Unlike the ‘natural’ conditions of a koi farm pond, where koi can graze and forage all day, and where snacking is actually encouraged, our gin-clear, hyper-filtered ponds cannot satisfy the nutritional requirements of our koi. Put simply, if we don’t feed them a complete and balanced diet, they won’t get one, and their health will suffer as a result.

Not too much, Not too little

What do we mean by a balanced diet? A diet is described as balanced when all of the constituent parts are neither limiting or excessive relative to an animal’s nutritional requirements.

Consequently, each animal requires a different balanced diet. If the diet is deficient in a particular area, or excessive in others, then prolonged exposure to such a diet will cause health problems. ‘Fast food’ is not bad for us, as long as it is part of a balanced diet.

A complete diet is on that fulfils all of the nutritional requirements of an animal, and it is our responsibility to provide any captive-reared animals complete nutrition, be they in a zoo, aviary or koi pond.

To be able to fully appreciate how a diet can influence the health of koi, we need to analyse the components of a healthy diet in the light of the functions each part of the diet plays. Furthermore, it is necessary to understand how koi breakdown and utilise each component.

Components of a koi diet.

Artificial koi foods can contain a wide range of raw materials in their formulation and these can be blended to provide an overall balanced diet. The formulation of a balanced diet must contain the correct quality and quantity of the various nutrients groups. These are Proteins, carbohydrates, lipids, vitamins and minerals.


Protein is very important to koi, as it is the only nutrient to provide growth. It is also the most significant contributor to the price of a diet.

Koi require protein for growth, repair of damaged tissue and the production of sperm or eggs. Proteins are made up of soluble building blocks called amino acids. There are 24 amino acids, with koi requiring 10 essential amino acids in their diet. They are able to manufacture the remainder themselves. Raw ingredients such as fishmeal, poultry meal and wheatgerm are included in the diet as high quality sources of these essential amino acids.

Protein requirements decrease with the age of koi, but increase with the water temperature. Juvenile koi that are actively growing require high protein diets of 30-40% to fuel such rapid growth whereas larger koi on a maintenance diet will require less protein in their diet. Similarly, as the temperature increases, so do the koi’s metabolic rate and its demands for energy and protein.


Carbohydrates are vegetable in origin and include the complex sugars such as starch. They also include cellulose (fibre) as a source of roughage which assists the movement of food through the gut. To keep waste in ponds to a minimum, artificial koi diets will have a reduced fibre content compared with their natural diet.

Carbohydrates are included in high quantities in koi diets as a source of energy. Too little carbohydrate in the diet may lead to koi using the relatively expensive protein as a source of energy. This will lead to a drop in growth rate and an increase in ammonia excretion which may cause the water quality to deteriorate. Too much carbohydrate (an energy) in the diet can lead to fish putting on fat causing a detrimental change in bodyshape.


Lipids (oils and fats) are used by koi as a source of energy. They also play an essential role in the formation of cell membranes and are carriers of the fat-soluble vitamins A, D, E and K.

Lipids are included in the diet as fish or vegetable oils. The oil content of a koi diet should be less than 10% as excessive oil levels can lead to koi health and water quality problems. This is one of the reasons why koi should not be fed exclusively on trout pellets that are traditionally very oily. It is essential that koi are fed unsaturated lipids (oils) that remain liquid at low temperatures. If koi are fed saturated fats then dietary problems are likely to occur as they are unable to utilise large quantities.


Koi require vitamins in their diet to carry out essential functions for healthy growth. Vitamins are complex organic substances that are required in minute quantities. A number of vitamins are notoriously unstable and may have to be supplemented by adding premixes during the manufacture of pellets to guard against deficiencies. These will deteriorate over time, so keep an eye out for ‘best before’ dates on food.


Minerals are inorganic compounds required in the diet to aid metabolic functions and the deposition of tissue such as skin, scales and bone. They are also required in small or trace amounts and are included in the diet in the form of ash. Koi have the luxury of obtaining minerals from either their diet or the pond water. Something we cannot do.

Koi pellets may also be formulated to include a number of additives to improve or enhance various functions of koi.

Stabilised Vitamin C

Vitamin C is vital in the diet for fish health, fighting disease and repairing damaged tissue. The fragile nature of vitamin C means that it can be lost during the manufacture of expanded koi pellets. As koi are unlikely to obtain vitamin C from within a koi pond it must be included in the diet to maintain health and to prevent the occurrence of deficiency problems. A stabilised form of vitamin C is now an important additive to many koi foods that will remain unchanged through the manufacturing process and prevent deficiency problems in koi.

In summary, the health and vitality of our koi rests in our hands. We should be satisfied that the food offered to our koi provides all they need to remain healthy. Check the labelling for vitamin declarations and best-before dates and that there is a good balance between animal and vegetable ingredients.

Kill blanketweed and string algae.