Koi nutrition and food. Back to basics

Koi are just like any other fish or animal in that they have particular nutritional requirements. After water quality, koi nutrition comes a very close second to having the greatest influence on the health and appearance of koi.

A koi’s diet will affect its growth, colouration, resistance to disease and its breeding performance. Any deviation away from a koi’s nutritional requirements will not only be our personal responsibility, but also to our ultimate cost with inevitable downturns in health, vitality, growth and colour.

The artificial koi diet.

Koi are omnivorous, feeding on items that are either animal or vegetable in origin. These inquisitive fish constantly scavenge over a natural pond bottom feeding throughout the day, making the water muddy as they dig around. Readily consumed items include worms, insect larvae, algae, plant roots, shoots and other detritus (both dead and alive) that may have settled on the pond bottom.

But as koi are traditionally kept in a densely stocked pond, they are completely dependent on us to provide them with a suitable artificial diet. It is not practical or economically viable for us to feed our koi on naturally occurring foods such as daphnia, bloodworm and fresh vegetable matter.  Problems would arise with the season availability of say daphnia, which would also need to be collected on a regular basis (if some could be found). However, because of many years of nutritional research across the world, it is possible for our koi to obtain a complete and balanced diet from a dry artificial food.

Complete and Balanced.

Complete and balanced mean two different things when describing a diet. If I went to a fast-food burger bar and ordered a quarter pounder with all the trimmings – then I could argue that this was a complete food. That is, it contains something of all the nutrients that we require to remain healthy. However, the bad press that fast-food restaurants have been receiving recently is due to the food being unbalanced. That is, even though all the nutrients may be represented in their food, they are not in the correct ratios or quantities. So that if you consumed nothing but that diet, you would experience health problems on account of its unbalanced nature. The same is true for our koi. If we endeavour to locate a complete and balanced diet then they will thrive. If we don’t, then in essence we are guilty of sending them to a fast-food restaurant for every meal – with the very predictable consequences.

Key things to look for in a food.

All reputable koi foods will contain the 5 nutrient groups (see Boxout), providing adequate balanced nutrition for your koi and pondfish however there is no industry standard that koi food must meet before it can be sold.

Carry out some detective work yourself before buying. Look at shop displays to spot which are the popular foods and ask friends and aquatic retailers which food they use or would recommend.

When choosing a food it is also wise to keep an eye out for the following. These may often set different foods apart and may be reflected in the price.

1. Value for money. Check and compare weights. This may sound obvious but different foods will have different densities – some being more ‘blown’ with air than others. This may give the impression of getting a larger pack for your money when in fact you may be paying for air!

2. Look on the ingredient list for a wide range of ingredients and for beneficial additives such as:

Colour enhancers. Raw ingredients such as spirulina, krill, marigold meal and other synthetic compounds such a astaxanthin and canthaxanthin are included to enhance the skin colouration in koi. A food containing these will improve your koi’s colour but will also increase the price of the food.

Stabilised Vitamin C. Most of the natural Vitamin C is lost in the manufacturing process. Stabilised Vitamin C is added to provide a boost of such an essential Vitamin ensuring your koi are kept in tip-top condition.

3. Packaging. Is the packaging robust and re-sealable enabling you to keep the food fresh for a reasonable period? If food is left open to the air then it’s quality will rapidly deteriorate.

4. Best before date. Make sure that you are buying this year’s stock and that the ‘Best Before’ date will last until the end of the season. Vitamin content should be present up to 18 months after manufacture. The less time there is on the best before date the less fresh the food is.

What different forms and types does koi food come in?

Just as we can order our eggs fried, scrambled, poached, or boiled (soft or hard), we can also buy our koi food in different formats. Equally, just as an egg’s nutritional content will largely be unaffected by how it is cooked, we can offer our koi exactly the same diet in different formats. The choice available is largely due to koi keeper preference.

The different koi food formats can be divided into 3 groups.

1. Floating Pellets & Sticks

2. Sinking Pellets

3. Paste Foods

Each food format offers a number of benefits to both koi and keeper, and can be considered for a number of practical reasons.

1. Floating pellets & Sticks

Floating pellets (or expanded pellets) are produced through a process called extrusion. Food ingredients are milled into a fine flour and heated into a paste which is then forced through a set of holes which determine the pellet diameter. As the warm paste is pushed through the holes under great pressure, they expand and take on air, creating a honeycomb of microscopic voids within its structure which makes the pellets light enough to float. A series of knives then cut this expanded sausage of paste into pellets which are then divided into the pellets we feed our koi. Floating pond sticks are made in a similar way where the knife cuts less frequently, producing a long stick rather than a more compact pellet.

Besides offering all of the benefits of an artificial diet as outlined earlier, pellets are also probably the best means of keeping leaching to a minimum. Due to the low surface area to volume ratio, pellets will absorb little water when consumed quickly, ensuring that koi benefit from a complete diet. Floating diets also allow us to interact with our koi and spot any individual fish that may not show an appetite. Thus feeding a floating diet can allow us to spot some health problems at an early stage.

2. Sinking Pellets.

A sinking version of a floating pellet can be manufactured in a similar way by preventing the pellet from expanding and taking on air during extrusion. As the resultant pellet is denser than water, it will sink.

Sinking pellets offer koi the ability to feed off the pond bottom (if the pellets actually reach the pond bottom before being eaten). They are a departure from the traditional floating pellet and should be used with care as any uneaten food may go unnoticed. Sinking pellets also do not bring the beauty of koi to the surface or allow us to see whether all koi are feeding. However, a sinking diet can be offered as a first food in the spring to encourage any reluctant feeders to come out of their winter slumber.

3. Paste Foods

Paste foods are produced by intercepting the finely milled ingredients prior to them reaching the extruder. Paste foods must be mixed with water to form a firm dough ball that can be offered, a piece at a time, to koi. Paste too is a sinking diet which rapidly stimulates the interest of all the koi in a pond. As soon as a paste is mixed with water, water soluble ingredients leach out into the water, alerting the koi’s acute olfactory (smell) senses that there is food about. The benefits of paste foods is that they are soft and moist and create frenzied feeding activity. However, they require mixing (creating twice their dry weight once mixed) and can cause a little clouding during feeding time (nothing an adequate filter cannot handle). Due to the issue of leaching caused by the fine nature of the paste flour, there is a risk of koi receiving a deficient diet unless precautions are taken during formulation.

Boxout: What are the 5 nutrients:

Whatever the blend of raw materials in a koi diet, they must satisfy specific criteria to provide a complete and balanced diet.

  • Protein.  Levels of approximately 30% are typical but will be higher if a growth food and lower than this if a low temperature food. Protein is present for growth and repair and is the diet’s most costly ingredient. Sources of protein include both animal and plant derivatives and meals such as fishmeal, soya, wheat and egg.


NB No mammalian proteins (cattle, sheep etc) are permitted in koi diets in the EC through the BSE legislation!

  • Carbohydrate.  These are the complex sugars such as starch and cellulose. They are all plant in origin and are included in high quantities in koi diets as an economical source of energy. They are also included as a source of fibre to aid digestion.


  • Oils. Oils are included as fish or vegetable oils. Usually less than 10% in the diet they are used by koi for energy and in the production of new tissues etc. If too much oil is included then pellets appear greasy and oily as in a trout pellet. These tend to be too rich for koi and can cause water quality problems.


  • Vitamins and Minerals. Manufactured diets often rely on the natural vitamin and mineral content included in the raw ingredients. More recently better quality brands have been including stable supplements of the notoriously unstable Vitamin C.


Boxout: Different Formats and Types of Food

Different Formats

1. Pellet           (baby, small, medium, large)   – Floating

                                                                        – Sinking

2. Stick                                                                        – Floating

                                                                        – Sinking

3. Paste

Different Types

1. Growth:                  High protein, summer diet

2. Wheatgerm:            Low protein, low waste diet – traditionally for low


3. Staple:                     All round food. A complete and balanced ‘maintenance’ diet’

Boxout: Choosing Food

Factors to consider when choosing a food.

  1. Is it complete and balanced?
  2. Is it in the correct format for your preference? (Pellet (s/m/l), Stick, Sinking/Floating
  3. Does it offer good comparative weight-for-weight value?
  4. Is it the right formulation for the time of year?
  5. Does the best before date have long enough to run?
  6. Is it the correct quantity for your needs? i.e. not too much. If you buy too much, once opened, it could deteriorate before you use it all.
  7. Ask fellow koi keepers or your koi dealer what they use or recommend.
  8. If you want colour enhancement – check to see it contains the relevant ingredients.

Kill blanketweed and string algae.