Feeding koi should not simply be regarded as satisfying their hunger. It is an opportunity. We have seen that a koi’s diet is instrumental when endeavouring to improve their health and growth. The final of the 3 most desirable characteristics that can be enhanced through their diet is colour.
Myth, mystery and even magic formulations abound when the topic of feeding for colour is discussed. True, there are some closely guarded secrets and practices that professional breeders will not disclose (Coca-cola style) but colouration and pigmentation in koi is controlled by a number of well established research-backed physiological processes. So just as we can work with a koi by feeding to enhance their health and growth, science dictates that we can do the same for colour.
A koi’s colouration is determined by the interaction of a combination of internal and external factors.
Internal factors: The koi’s genetic make up inherited from its valuable brood parents will code for the colour, distribution and development of a koi’s pattern. The internal factors will only be expressed if the koi are offered an appropriate diet (in the same way that recent research shows that where obesity is caused genetically, it will only be expressed if the individual consumes the necessary quantity of food).
External factors: Besides other factors, the most important external factors that influence koi colour include water quality and specifically, their diet.
The roles of colour enhancers.
Koi are only able to exhibit pigments if they receive them (or their precursors) in their diet. Each type of chromatophore in the skin stores and exhibits a different carotenoid (a group of natural pigments). For example, a melanophore will store black pigment while erythrophores will store red pigments and only those colours that a koi exhibits can be enhanced by feeding a carotenoid-rich diet. Carotenoids are organic, unstable compounds that are closely related to Vitamin A, imparting colour by the way they absorb and reflect light. Those pigments at the lower end of the spectrum (lutein) will produce yellow pigmentation while those higher up the spectrum (astaxanthin) will produce the more desirable red pigmentation.
As carotenoids degenerate over time (in the same way as vitamins) koi colours can fade. In the same way as a car needs to be topped up with petrol to keep it running, so a koi’s colour-tank needs to be kept topped up for a koi to maintain its vibrant colouration.
Carotenoids are, of course, not unique to the world of koi. They occur naturally in a range of natural products from tomatoes, peppers, flowers, insects (ladybirds – cochineal food colouring) and many aquatic organisms such as lobster and krill. They are synthesized by plants and algae and then passed up the food chain. For example, marine algae will be consumed by filter feeding crustacea, which inadvertently pass on their pigmentation to wading flamingos which will adopt a similar pinkish colour.
The algae consumed by krill will be rich in pigments such as carotene, lutein and zeaxanthin (which are definitely not pink) and upon assimilation, krill are able to convert these carotenoids into the red pigment astaxanthin (named after the lobster – Astacus).
Crafty Koi
Koi too are quite cute when it comes to manipulating colour enhancers. Like krill, they are able to convert pigments commonly found in algae (spirulina) such as lutein and carotene into the more desirable red pigment astaxanthin. (Something trout and salmon are unable to do, requiring astaxanthin to be included in their diet if their flesh is to take on a pink appearance). Also if a koi’s chromatophores express yellow pigment (as in a Yamabuki) then koi will exhibit the same yellow pigments from spirulina unchanged in their skin. When stripping ripe female koi of eggs, each koi will release eggs that differ in colour, even though they will have been fed the same diet. This is further indication that individual koi can manipulate and express different pigments that they assimilate from their diet.
Sources of carotenoids that koi can utilise to enhance their colouration.
Recognising that koi colour is most intense in a natural clay pond environment, we are able to mimic the colouring effects of their natural diet to an extent by including similar additives to their artificial diets.
There are two approaches to enhancing colouration in koi. The broad-brush approach (using the breadth of carotenoids available in natural sources) or the more deliberate and precise approach (using synthetic colour enhancers).
Natural sources: There are several recognised natural sources of carotenoids suitable for colour enhancement. Like any natural commodity, qualities and pigment content can vary from source to source, and being organic, can be liable to degradation during food manufacture. However, natural sources are also renowned for offering a superb range of carotenoids giving koi (who have the ability to convert carotenoids)excellent colour potential. For example, marigold petals have more than 20 different carotenoids, which koi can work with and manipulate. They also have a high concentration of these compounds (approximately 9000mg per kilo), whereas shrimp or krill meal will only have about 200mg per kilo, with the added issue of the exoskeletal material having an exceedingly high ash content.
Furthermore, there is a price to pay for koi using natural carotenoid sources as the process of converting them into more desirable astaxanthin requires energy.
Artificial sources
Aware of some of the limitations with natural sources of colour enhancers, much research has led to the formulation of potent, stable and effective man-made colour enhancers. These will provide koi with a precise amount of pigment in the form in which it will be deposited in the skin. So rather than feeding a natural source of unknown quantity or quality of carotenoid which koi will convert into red, they can be offered a metered dose of pigment in the final form in which it will be used.
Look for foods with the following ingredients as they will enhance the colouration of your koi.
Top colour enhancing compounds:
Marigold Flower Meal. Probably one of the most potent natural sources of carotenoids available. The pigments require manipulation by koi to convert them into reds.
Artificial Colour Enhancers. Astaxanthin and Canthaxanthin are guaranteed, potent sources of colour in the form that will be exhibited immediately in the skin.
Spirulina. This has an above average carotenoid content that is easily assimilated, being found in very simple algae cells
A Yeast – Phaffia rhodozyma. This is easily digested and is a recognised source of carotene and astaxanthin.
Paprika. Red Pepper Meal. More potent than spirulina, and contains red pigments ready to be absorbed and assimilated immediately.
Other environmental factors
Managing the water quality to complement the effects of a colour-enhancing diet is likely to lead to further improvements in colour.
Colouration and skin quality improves greatly in harder more alkaline waters where the ready supply of minerals enhances darker pigmentation and improves the lustre of the guanine-rich iridocytes. The regular dosing with a high quality calcium montmorillonite clay and the buffering of the water with a calcium rich substrate will be effective in producing a mineral-rich pond environment.
In summary, when seeking to enhance the appearance of koi, we can only work with what we’ve got – that is the ‘internal’ genetic code that koi have inherited from their parents. While many sources of colour enhancers are available, some obviously outperform others due to their quality and composition of specific carotenoids. Scientific understanding of how carotenoids work in partnership with a koi’s colour potential has lead to the production of potent synthetic colour enhancers that have a precise and predictable effect on koi.
Where does all the colour come from?
Colour and pattern in koi is produced by clusters of tiny microscopic colour cells called chromatophores
Types of colour cells.
There are two groups of colour cell situated in the skin – those that are coloured and can be enhanced and those are not coloured.
A koi’s appearance is determined by the interaction between the group of cells called iridocytes (which are packed with guanine to reflect light, giving the koi a metallic lustre) and those cells which exhibit a specific colour and can be enhanced by feeding a colour enhancing diet. These include the black melanophores (sumi) which also produce blue when set deeper in the skin, and the erythrophores (hi) which give a koi an orange or red colouration.
