As we saw in the previous article, 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 5 nutrient groups.
Artificial koi foods can contain a wide range of raw materials in their formulation. These will be blended to provide an overall balanced diet. The specification of a 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 that provides growth. It is also the most significant contributor to the price of a diet.
Fish 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, soya and wheatgerm are included in the diet as high quality sources of these essential amino acids.
A koi’s protein requirement decreases with the age of a fish, but increases with the water temperature. Juvenile koi that are actively growing require high protein diets of 30-40% to fuel such rapid growth whereas larger fish on a maintenance diet will require less protein in their diet. Similarly, as the temperature increases, so does a 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 pond diets will have a reduced fibre content compared with their natural diet.
Carbohydrates are included in high quantities in koi foods as a source of energy. Too little carbohydrate in the diet may lead to your koi to use 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 (see later). Too much carbohydrate (and energy) in the diet can lead to koi putting on fat causing a detrimental change in bodyshape.
Lipids (oils and fats) are used by koi as a source of energy, although the oil content of a koi diet compared to other energy sources is very small. 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 food 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 your koi should not be fed trout pellets or other oily foods. It is essential that koi are offered unsaturated lipids (oils) that remain liquid at low temperatures. If they 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. Vitamins 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 declared in a diet’s analysis as ‘ash’ (even though ash itself is not an ingredient). Your koi have the luxury of obtaining minerals from either their diet or the pond water – Something we cannot do.
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.
Box Out: 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.
Box Out: Protein : Energy balancing a diet:
Diet 1. A protein : energy balanced diet. The ideal koi food.
A. Protein is used for growth
B. Carbohydrate is largely the energy component, and is used as a clean source of energy = better water quality.
Diet 2. An unbalanced diet. Too much protein relative to the amount of energy in the diet. This might be typical of a natural carp diet, but will cause problems in a densely stocked pond.
A. Protein is used for growth
B. Protein is also used for energy (as there’s lots of it and little energy available elsewhere in the diet) – high risk of high ammonia excretion
Diet 3. An unbalanced diet. Lots of energy relative to the amount of protein in the diet. This might be typical of a wheatgerm (low temperature diet).
A. Results in poor growth
B. Low risk of pollution