Koi Nutrition: How different ingredients are used to formulate different types of food.

Our koi depend upon us for a complete and balanced diet. That is, a diet that not only provides them with all the nutrients required for health, growth and colour, but also in the correct quantities. Besides including all of the nutrients that koi require, two other aspects of advanced koi food formulation are required to promote good koi performance, as well as pond performance – recognising that the food we feed our koi will influence the water quality. These are how a koi food must be balanced with respect to the energy in the diet and how a diet is best formulated to help to safeguard the pond’s health through reduced ammonia excretion.

The Five Nutrient Groups

Artificial koi foods are formulated from a range of raw materials blended to create a balanced diet. To support health, growth and vitality, a feed must provide the correct quality and quantity of five essential nutrient groups:

• Proteins

• Carbohydrates

• Lipids (fats and oils)

• Vitamins

• Minerals

Each group plays a specific and important role in koi nutrition.

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Protein

Protein is the most important nutrient for growth and is typically the most expensive component of a koi diet.

Koi require protein for:

• Growth

• Tissue repair

• Reproduction (egg and sperm production)

Proteins are made up of smaller building blocks called amino acids. There are 24 amino acids in total, of which koi require 10 essential amino acids in their diet. The remaining amino acids can be synthesised internally.

High-quality protein sources such as fishmeal, soya and wheatgerm are included in koi feeds to ensure adequate levels of essential amino acids.

Protein requirements vary:

• Juvenile, rapidly growing koi require high-protein diets (typically 30–40%).

• Mature koi on maintenance diets require less protein.

• Protein demand increases with rising water temperature, as metabolic rate increases.

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Carbohydrates

Carbohydrates are plant-derived energy sources and include complex sugars such as starch. They also provide fibre (cellulose), which aids digestion and supports gut movement.

Commercial koi feeds often contain reduced fibre levels compared to natural diets, as excessive fibre increases waste output and can negatively affect water quality.

Carbohydrates are included in significant quantities because they provide energy efficiently and economically.

If too little carbohydrate is supplied, koi may use expensive dietary protein as an energy source instead. This results in:

• Reduced growth

• Increased ammonia excretion

• Potential water quality deterioration

Conversely, excessive carbohydrate intake can lead to fat deposition and undesirable changes in body shape.

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Lipids (Fats and Oils)

Lipids provide a concentrated energy source, though they are typically included at lower levels than carbohydrates.

They are also essential for:

• Cell membrane formation

• Absorption of fat-soluble vitamins (A, D, E and K)

Lipids in koi diets usually come from fish oils or vegetable oils.

The oil content of koi food should generally remain below 10%. Excessive oil can contribute to both fish health issues and water quality problems.

This is why trout pellets and other high-oil feeds are unsuitable for koi.

Koi require unsaturated oils that remain liquid at lower temperatures. Saturated fats, which solidify more readily, are poorly utilised and can lead to digestive problems if fed in excess.

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Vitamins

Vitamins are organic compounds required in very small amounts but are essential for normal metabolic function and healthy growth.

Some vitamins are unstable and degrade over time, particularly when exposed to heat, light or moisture. For this reason, manufacturers often include vitamin premixes to ensure adequate levels in the finished pellet.

Because vitamin levels decline with age, always check “best before” dates when purchasing koi food.

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Minerals

Minerals are inorganic compounds required for:

• Metabolic processes

• Bone formation

• Skin and scale development

They are needed only in small or trace amounts. On feed labels, minerals are often declared as “ash” — representing the total inorganic content remaining after combustion (though ash itself is not an added ingredient).

Unlike humans, koi can obtain minerals both from their diet and directly from the pond water, giving them a unique nutritional advantage.

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A well-formulated koi diet balances all five nutrient groups according to fish size, water temperature and growth stage. Understanding these components helps ensure optimal fish health while maintaining good water quality.

What makes a summer food different from an autumn food?

As summer is the warmest period of the year it is the period when fish will utilise their food for both growth and storage of energy for the fallow winter period. Consequently, such diets are high protein and high-energy diets, ready to satisfy their increased nutritional demands.

Right diet – wrong time

If a high protein growth diet is offered when your koi cannot utilise them efficiently (i.e. at low temperatures), then levels of excretion will be increased having a knock-on effect on water quality. Excess protein in particular is likely to affect water quality.

It’s all in the balance.

If protein in the diet is in excess of what your koi require, they will not utilise all of the protein in the diet for growth, but either break it down and burn it for energy or excrete high levels undigested. This is highly undesirable – and is something that advanced koi formulations address.

How do you make a koi food that is protein:energy balanced so that the protein is used optimally for growth, and ammonia excretion is minimal?

Koi can use the protein we feed them in a diet in one of two ways:

– For growth – which is most desirable
– For energy – which is undesirable

We do not want our koi to use our valuable protein for energy as this means they will not be using it for growth. Also, burning protein for energy will lead to excessive and harmful ammonia excretion.

Protein is made up of 4 elements, carbon, hydrogen, oxygen and nitrogen. When protein is used as a source or energy, koi utilise the carbon, hydrogen and oxygen element but excrete the nitrogen in the form of ammonia. Consequently, too much protein in the diet is likely to lead to an increase in the levels of ammonia excreted by koi.

So we need to look into cleaner sources of energy for our koi, that once ‘burnt’, do not put our water quality at risk through excessive ammonia excretion.

The answer is to use carbohydrates. From their name you might be able to guess that carbohydrates are made up of carbon, hydrogen and oxygen (and no nitrogen – unlike proteins). This means that when they are burnt, there is no nitrogen (ammonia – NH3) by-product to pollute our water.

Protein Sparing.

The whole process of incorporating alternative ‘cleaner’ sources of energy to protein in a koi diet is called ‘protein sparing’ as it spares protein for growth. A carp’s natural diet is likely to be in excess of 50% protein, a good proportion of which will be used for energy – with the knock on excretion of ammonia. However, because the stocking density of natural waters is so much lower than a koi pond – there is no real problem with this natural approach to gaining energy. It would be an issue in a koi pond – that’s why we reduce the protein content and increase other sources of energy – sparing the protein just for growth.

Look out for the following ingredients and see what their function is in the diet.

1. Fishmeal, poultry meal, wheatgerm , maize gluten – Protein sources used for growth, tissue repair, sperm/eggs production and energy
2. Wheat, Bran, Rice, – Carbohydrate sources used as a source of energy
3. Fish Oil – Oil source used in cell membranes and for energy.
4. Ash (mineral / inorganic element). Although not an ingredient, an ash declaration is made on koi food labels and is a means of measuring the inorganic (mineral) element of the diet.
5. Vitamins – Used in bioprocesses and to promote overall health and healing. Look out for Vitamin C being declared on the analysis.
6. Spirulina, Krill, Marigold, Astaxanthin, Canthaxanthin – Carotenoids used to enhance colour.