C: Pond keepers A to Z … Carp to Colour Enhancer

Carp This is where it all started.


A dull, black/grey food fish with a natural geographical range of Asia and the watershed of the Black and Caspian Sea.

It is quite easy to take koi to be a new species developed by man when we see how different in bodyshape, colour and vitality they are compared with their wild ancestors. Yet, technically, and largely biologically, koi are still the same carp species (sharing the same scientific name Cyprinus carpio) as their ancestors with the ability to cross back with standard carp to produce viable offspring; and a mixed bag at that.

The carp thrives in deep, slow moving waters where there are abundant water plants and soft, silty sediment.

Carp act as the ‘Hoovers’ of the pond, grubbing around for insect larvae, snails, crustaceans and plants. They have an acute sense of smell and are easily ‘spooked’ with their acute sensitivity to vibrations. However, they are also easily domesticated and can become very tame, growing to a large size and a ripe old age.

All this should sound familiar to koi keepers as well; showing that beneath that enigmatic skin, koi are largely in effect still carp. It can be a valuable exercise to remind ourselves every now and then that koi are carp as this can give us a better insight in to their environmental needs.

For example, if the carp is an opportunistic ‘grazer’, constantly sampling and tasting the sediment for food, feeding regularly throughout the day, why do we feed them like predators, forcing them to eat their fill in 5 minutes each day? It is no surprise that growth and feed efficiency are improved through regular feeding. Fortunately for us, a feature of carp is that they are adaptable, tolerant and intelligent fish, often adapting to our ways when in fact it should be the other way round.


These compounds are added to our domestic water supply as a disinfectant. However, chlorine and chloramine are toxic to fish. It is easy to detect chlorinated water, especially when running the cold tap full bore for a minute or so. A good nostril full will take you back to outings to the swimming baths.

Great! The water supply companies are providing us ( and our fish) with germ-free water with no health risks. But unfortunately, the chlorine and more persistent chloramine perform their disinfecting role discriminately both on target bugs and non-target areas such as sensitive gill tissue.

Avoiding Chlorine/Chloramine toxicity in the pond.

Add a tap water conditioner when making a water change with raw tapwater

Use an in-line water purifier that will selectively remove chlorine and chloramine contaminants as well as other pollutants

Use an alternative source of water e.g. rain, well, borehole water. However, depending on the precise source, these too may offer a number of other water quality problems.

College Course.

If through keeping koi you have definitely got the aquatic bug, or perhaps you were just fish crazy to start with, then what can you do to reach your full potential? Why not investigate a course that allows you to learn more about the finned aquatic creatures or even turn your hobby into a career?

We are never too old to learn and you will have just as much experience to pass on to others as the course will to teach you. There are courses in Fish Farming (including koi and carp) and Aquatics with excellent track records in fulfilling peoples’ expectations and preparing them for that opportunity to turn their hobby into a career.


This is one of a host of protozoan parasites that can cause irritation and a flicking and flashing response in addition to a loss of colour through the production of a milky film on the body surface.

Chilodinella feed on skin tissue and mucus, irritating koi by their roving presence on the exterior of fish. A case of chilodinella can only be confirmed through a microscopic examination of a mucus scrape, spotting the ‘whirly-gig’ motion of the pear-shaped Chilodinella organisms under high magnification. The medication is quite straight forward, using a recommended proprietary brand’s treatment.


(Now called Ichthyobodo) Costia is the old name for this protozoan parasite, now named Ichthyobodo. It is similar in its symptoms and treatments as Chilodinella. As with most protozoan parasites, they are generally opportunistic organisms, present in low, sub-lethal levels, ready to take full advantage of a fish in a stressed state. Stress may result from overstocking, overfeeding or poor water quality. Usually, an outbreak in disease can be traced back to mismanagement on our behalf.


Unless you don’t make the grade!

Culling is the less glamorous side to koi keeping and is the selective removal of poorly coloured, poor quality fish common to every koi spawn.

A feature of the genetic ancestry of koi means that whenever koi spawn, there will be a significant number of fry that do not resemble their parents, but more the inferior colour and pattern of the original broodfish many generations before.

In complex varieties, such as sanke, kohaku and showa, these ‘throwbacks’ are generally ‘peach coloured’ lacking pattern or definition. Culling is a labour intensive, back breaking operation involving any available and experienced hands (usually the whole family) and occurs at set intervals throughout the development of koi. The first cull is a general cull and may occur at the fry stage (up to 4 weeks old). Those fry that exhibit physical deformities or are the wrong colour for that variety are culled at this early stage.

However, the most effective cull is after a further number of weeks growth and development in a mud pond, when the pond is netted and the fry at 1/2 – 1″ are inspected one at a time for desirable colour variation and pattern. As patterned fish are the exception rather than the rule, the time saving technique used while culling is to place a hand-net full of hopefuls into a bowl (washing-up size) and pick out the desirable few. The others are discarded, never to be seen again. Culling ensures that valuable pond space is used to its maximum potential, so that the stocking rates are as low as possible for the selected and valuable fish, ensuring their rapid growth and development.

Carp Pox.

Carp pox is a viral infection showing itself as a number of random white, grey or pink wax-like growths on skin and fin tissue.

The growths are proud of the skin and at times may often take on the colouration of the surrounding tissue. Carp pox is usually a spring phenomenon, infecting a weak fish coming out of its winter break. Although the wax-like tumours are very unsightly, carp pox does not appear to adversely affect fish health and may only infect single fish in a well stocked pond.

Affected fish appear to overcome the symptoms themselves as the water temperature rises and fish metabolism picks up to fight off the virus with an enhanced immune response.

As it is caused by a virus there is no reliable treatment and its occurrence although alarming is no reflection on the husbandry your fish receive. In some way, carp pox can be compared to warts in humans as there is no apparent reason why they appear and they can disappear as quickly as they appeared.

Colour Enhancers (Carotenoids)

We are what we eat, and the colour of many pond fish can be enhanced by the diet that they eat.

Colour enhancers, or to give them their specific name, carotenoids, are naturally occurring pigments that if included in the diet can be incorporated into the skin to enhance existing colours. For example reds and oranges can be enhanced to become deeper and more vivid.

A natural pond environment and its natural flora and fauna are full of natural colour enhancing pigments. This is one of the reasons why koi, orfe and goldfish often show their colours best having spent some time in a natural mud pond environment.

In our clear, more hygienic garden and koi ponds, such a naturally occurring colour enhancing diet does not exist, so their colours can only be enhanced by providing carotenoids in their food.

Ingredients that are included in a diet for their colour enhancing properties include: Spirulina, a single-celled algae that enhances red pigmentation. Krill, a crustacean that is pink through its colour enhancing properties. Salmon flesh is coloured pink by virtue of a salmon’s krill and crustacean rich diet. Marigold petals, high in a wide range of colour enhancers. Lobster eggs, a reliable and quality source of carotenoids.

Did you know?

Specific natural additives can be added to the diet of hens to enhance the yellow colour of the yolk. Some koi foods even contain purer and more concentrated forms of the carotenoids, manufactured to produce excellent results. Besides quality koi diets, these are also used in trout and salmon foods to colour the flesh pink and to make them look like wild rather than farmed fish. Two such potent colour enhancing compounds include astaxanthin and canthaxanthin.

Kill blanketweed and string algae.