It is essential that pond fish and koi are fed a diet containing a balanced source of quality and highly digestible protein.

What is the role of protein in koi nutrition?

Proteins are important in the diet as besides being required for growth and repair of body tissues, they also represent the most expensive part of the 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 of which there are 24, 14 of which can be synthesised by fish. The other 10 amino acids which koi are unable to synthesise are classed as essential amino acids and must be supplied in the diet in high quality protein feedstuffs e.g. fish meal, poultry meal and wheatgerm. If a diet is deficient in any of the 10 essential amino acids then the growth and development of the fish will be retarded.

As fishkeepers, it is our responsibility to provide the best food we can for our fish and we do not want to feel that we are depriving our fish of the best.

The higher the protein, the better the food?

Fish in their natural environment are likely to consume a diet in excess of 50% protein which is used:

(a) as a source of energy

(b) for new tissue growth and repair

So why don’t artificial koi diets also contain in excess of 50% protein?

1. Price.
As protein is the most expensive part of the diet, a 50% protein diet would prove to be too expensive to feed koi. This is especially true when the protein is of a premium quality.

2. Water Quality.
Koi are unable to digest and utilise all of the protein in a 50% protein diet for growth. They will use excess protein as a source of energy. When koi ‘burn’ protein for energy instead of using it for growth, the nitrogen in the protein is not utilised but excreted as toxic ammonia. Consequently, it is wasteful and may cause water quality to deteriorate if koi are fed an excessively high protein diet.

What is the relationship between protein and energy in a koi diet?

Protein content of the artificial diet is set at a level so that it produces good growth but also so that it is not used as an expensive source of energy. Carbohydrates (sugars) and lipids (oils) are included in the diet as a cheaper source of energy to spare some protein. This is called protein sparing and it is used in all artificial diet formulations to produce a high performance diet at a reasonable price.

The protein in the diet must also be in balance with the energy in the diet. Too much protein and insufficient energy in the diet leads to protein being used as an expensive and inefficient source of energy. Too little protein in relation to the energy content of the diet leads to excess energy being laid down as fat causing physiological strains and ultimately obesity.

Why do Nishikoi® foods contain a range of different protein levels?

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. Similarly, as the temperature increases, so do the koi’s metabolic rate and its requirements for energy and protein.

For this reason, Nishikoi® Wheatgerm (20% protein) is formulated for feeding koi at low temperatures in spring and autumn when koi are not actively growing.

Nishikoi® Staple (28% protein) is formulated as a maintenance diet that provides koi with complete nutrition at higher summer temperatures with high quality proteins to enable the maintenance and repair of body tissues.

Nishikoi® Growth (37% protein) is designed to fuel rapid growth at summer temperatures. It is balanced with the energy content to avoid the loss of well proportioned bodyshape while the protein level is not too high to cause koi to utilise the protein as a source of energy. This would be wasteful and lead to an increase in the excretion of toxic ammonia.