Through extensive research, nutritionists have discovered that by adding certain ingredients to the diet, the colour of certain animals can be improved or enhanced. This is particularly true of koi and other pondfish.

Spirulina, marigold meal, alfalfa, krill and other curious products are often included in the diet as colour enhancers. In December 1999, there was even a report of a girl’s skin temporarily taking on an orange hue after drinking considerable volumes of a leading fresh orange juice.

What are they?

Colour enhancers are natural pigments which when fed in the diet enhance the colour of fish flesh or skin.

Carotenoids are the colour pigments responsible for enhancing skin colour some of which include: alpha carotene, beta carotene, astaxanthin and canthaxanthin. They are available in a range of natural products including algae, flowers, aquatic invertebrates and yeasts and some are also manufactured synthetically.

Generally natural sources of carotenoids provide a wide spectrum of colour enhancers producing good colour, however they can be quite unstable and prone to variations in quality. Synthetic colour enhancers provide a guaranteed content of specific carotenoids but do not offer the wide range of carotenoids found in natural products.

Colour enhancers are used widely in the salmon and trout industry where they are used to enhance the pink in flesh. Carp have the added ability of being able to convert some carotenoids such as zeaxanthin (orange/yellow) into the more desirable astaxanthin (red) in their skin, thereby enhancing the red colouration on the fish.

Great care and expertise is required in the formulation of colour enhancing diets to provide suitable quality carotenoids in the correct quantities. If koi are fed excessive amounts of xanthophyll and other specific carotenoids then previously unpigmented white skin can become ‘pink’ reducing the overall appeal and quality of the fish.

How do they work?

Fish skin contains colour cells called xanthocytes which contain pigment carrying chromatophores. Chromatophores can be divided into melanophores (black) and lipophores (coloured) which contain the carotenoid pigments.

The genetic make up of the fish controls the depth and colour of the pigments in lipophores. Colour enhancers improve the pigment concentration by laying down more carotenoids in the lipophores (colour cells).

The more carotenoids in the diet the better?

There is a limit to the quantity of extra carotenoid which can be stored in each lipophore and therefore a limit to the extent to which the colour of koi can be enhanced. Carotenoids cannot introduce new colours in lipophores which are not coded for genetically, i.e. an orange fish cannot be made red by feeding excessive quantities of colour enhancers.

In conclusion, good skin quality can only be achieved by feeding a high quality balanced diet while maintaining an optimum water quality environment. A good quality colour enhancing diet will contain a wide range of quality colour enhancers and improve the colouration on a healthy fish while not adversely affecting white areas.

Nishikoi® Growth, Wheatgerm and Sinking Pellets all contain a blend of natural and artificial colour enhancers.

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