Koi Nutrition for the Koi Keeper
# 2 – FACTORS AFFECTING KOI GROWTH
There are several critical factors affecting the growth of all koi - genetics, temperature, oxygen levels, the excretion of growth hormones and nutrition.
No matter what we do and irrespective of pond specifications, the vast majority of koi simply cannot grow much bigger than about 60 - 65cm. The number of jumbo koi in the world above 75 - 80cm is limited - relative to the number of koi available on the commercial market. This is one of the reasons for large, high-quality koi being very expensive.
Genetics
Genetics will determine the final size of the individual koi.
Individual genetically determined growth potential, which is influenced by bloodlines, is the great leveler of the playing fields when it comes to koi growth and the ultimate size the fish will attain. We tend to assume that all koi from a certain parentage will grow large. We assume that all koi have the potential to grow to a meter long. This is not true. Nature in her infinite variety and beauty has imbued each individual koi with certain characteristics through the genes that are passed on from parents to off-spring.
Each individual koi cannot reach a size greater than its individual maximum genetic potential, but the actual size that a koi will reach is ultimately determined by many environmental and nutritional factors.
Temperature
Temperature is one of the critical factors affecting koi growth rate. High water temperatures plus high protein diets (above 36% protein) will produce a faster growth rate. The lower the temperature, the lower the growth rate, in part because their metabolism is slower and their bodies cannot assimilate the nutrients in the food as fast as at higher temperatures. On the other hand, they will need to consume much lower levels of food (nutrients) at lower temperatures because their body metabolism slows down. Digestion enzymes and function changes at lower temperatures. Koi digest food poorly below 10ºC.
The optimal water temperature for koi keeping is 22 - 28ºC. At this temperature there is maximum growth for a given amount of food ratio. However, above this temperature there is a fall in the conversion of food to energy and growth because of the relative fall in available oxygen levels.
Oxygen
The amount of dissolved oxygen in the pond water will be one of the limiting factors in achieving growth in a koi. Dissolved oxygen is critical for the growth and health of koi. For koi to remain healthy, adequate oxygen levels must be maintained (typically at above 5 – 6 ppm). The higher the oxygen levels in the water the healthier the koi will be and the more efficient the bioconverter will work. Koi are extremely efficient at extracting O2 from water and can do so at very low levels. However, koi do well in water with dissolved oxygen levels above 6ppm.
The life functions of koi are similar to those of other animals in that they have muscles, skeletons, skins and internal organs which function in approximately similar ways. There is, however, one great difference between fish and land animals - fish live in water. More importantly to our circumstances, koi living in a pond, live in a limited volume of water. There is not endless fresh water with endless oxygen and fresh food, only the water in the pond surrounding the fish.
The whole pond system from the koi to the bacteria in the filter is completely dependant on oxygen for survival. All the various forms of life in the pond are competing with what is essentially a limited supply of oxygen. While the atmosphere has around 250000 parts per million (milligrams per litre) water has less than of 8 - 10 parts per million.
It is an undisputed fact that koi have better growth, live longer and their colours are brighter and more intense in oxygen rich environments. It is also an undisputed fact that biological filtration is more efficient and flourishes in an oxygen rich environment.
Growth Hormones
Koi, like all living organisms, have a limit to their growth potential. The growth of koi begins immediately after the eggs hatch. For the first few years of their lives they produce growth hormones within the body. This is the period of maximum growth potential. Without correct nutrition during this initial period of the fish’s life the creature will not grow to its full potential. The production of growth hormones gradually decreases after about 4 years. Around 5 – 7 years the growth is slowed. Many may still continue to grow until 10 to 12 years old but at a greatly reduced rate.
Nutrition
Good nutrition (in combination with temperature, oxygen, good water quality and genetic potential) from hatching, is possibly the most critical factor in achieving growth.
Underfeeding of quality food is one of the main reasons that maximum growth rate is not achieved in koi. This growth / nutrition link must be achieved early in the fish’s life during the period when the fish can grow rapidly.
Nutrition and Health
The continuous intake of food sources that have the various substances needed by living organisms is critical for the health of our koi. Koi need continuous quality food from a very young age.
Proper nutrition aids in the development of the immune system, strengthens the bones, stimulates the blood etc. etc. Food deficient in vitamin C for example, has been associated with poor growth, spine and blood disorders. Food with increased levels of vitamin C has been demonstrated to improve the general health as well as the healing time of sick koi.
Mention is made of vitamin C as an example because natural vitamin C degenerates very rapidly in fish food. In fact, only 90 days after manufacture, natural vitamin C may have degenerated to only 30% of its original strength. In extruded diets, more than 75% of what was mixed into the diet can be denatured in the extrusion process itself. Therefore, it is essential that a stabile form of vitamin C be used.
Some koi foods may be old before we receive them. Some koi foods are not date coded, therefore there is no way to determine how old it is - it may be 1 week old, or it might be 5 years old.
My Koi Are Not Growing?
If all the factors related to koi growth are in place and your koi are not growing then there are several possibilities:
1. The genetics is a limiting factor. That individual fish cannot and will not get any larger. Just as with humans so with the koi. Each individual grows to a different size.
2. The koi you have purchased is old. It may look young because it is small, but the fish is past the age when it has the capability to grow significantly.
3. There are excessive pheromones in the water. Pheromones can suppress the growth of other koi in the pond or even suppress the immune systems. Usually found in over crowded pond situations or in pond situations where fresh water changes (out) are minimal or not done at all. Try removing the koi that does not grow into a different pond situation. If it still does not grow then genetics is in all probability the answer.
4. Water temperatures are low or oxygen levels are low.
5. Physical crowding. Try removing some of the fish to give the others more space. Increase water changes. Increase filter size and turnover rates.
DEFINITIONS – B & C
Balanced Diet
A diet that has all the nutritional requirements, in the correct proportions.
Canthaxanthin
Canthaxanthin - a naturally occurring carotinoid used to enhance the red.
Carbohydrate
Carbohydrate is the general term for compounds such as sugars (animal energy storage), starches (plant energy storage) and cellulose (plant structural material) that contain carbon, oxygen and hydrogen. Many carbohydrates can be used as an energy source by animals, although some are difficult to digest and so release only small amounts of energy to the body Bacteria in the gut of animals are responsible for the digestion of plant materials by herbivores. Healthy guts of healthy animals contain bacteria.
Carcinogen
Any substance that either produces or accelerates the development of cancer.
Carotenoids
A group of yellow, orange and red lipid soluble pigments with a similar chemical structure to Beta Carotene. Some carotenoids may be converted to vitamin A by animals. Beta carotene is simply two Vitamin A molecules linked together. See also astaxanthin, canthaxanthin & spirulina.
Catabolism
Any destructive metabolism by which organisms convert substances into excreted compounds. Alternatively described as - the breaking down in the body of complex chemical compounds into simpler ones (e.g., glycogen to CO2 and H2O), often accompanied by the liberation of energy.
Color Enhancers
See : carotenoids – Astaxanthin - Canthaxanthin
Colorants
Colorants in koi food are used purely for commercial purposes – to make the pellet a certain colour. There is no nutritional value in colorants used to give the pellets an appealing look.