Koi Carp: The Ultimate Guide

Koi Carp: The Ultimate Guide

With years of knowledge and experience in handling and selling Koi Carp, we have put together a simple, but in-depth guide to explain everything you need to know about these popular fish. 

Whether you have an understanding already but need some further guidance, or you are a beginner and considering purchasing a Koi, we have the answers and information you need.

And, if we don't, get in touch with our expert, friendly team who will help you find the right fish, and products you need. 

What is a Koi Carp?

Koi Carp, also known as Nishikigoi, are very popular fish which are often kept in a pond or aquarium.

They are coloured varieties of the Chinese Amur Carp (Cyprinus rubrofuscus), and are kept as pets with beautiful decoration. Koi is a general group name for the colour variants of the carp, of which there are many varieties (much like pedigree dogs). 

The origins of the Koi Carp date back to 200BC, where the Amur Carp was brought to Japan as a source of food during the Chinese invasions. As with many animals, the Amur Carp experiences a level of natural genetic variation resulting in skin colour mutations. The Japanese selectively bred interesting colour variants to enhance the colours and patterning leading to the Koi Carp we know today. This resulted in the Amur Carp making its way off the food menu and into the highly sought-after pet trade, with breeding as we now know it commencing after the 1800’s.   

Where do Koi Carp come from?

The Carp (Cyprinus) is a large group of fish, which occupy most of Europe and Asia in many shapes and forms. As mentioned, the origins of the Koi Carp actually begin in China (as Amur Carp), and they are very much rooted in Japanese culture. 

The Chinese first demonstrated selective breeding of fish for colour with the Prussian Carp (Carassius gibelio) over a thousand years ago, which led to the development of the various forms of modern goldfish. Similar breeding techniques were then used by the Japanese in Niigata to enhance the colours of the Amur Carp in the 1800’s. These were largely undiscovered and engrained exclusively in localised Japanese culture until they were demonstrated at an exposition held in Tokyo in 1914. From there on, the interest in Koi Carp spread throughout Japan and eventually worldwide. 

Since then, selective breeding of Koi Carp has taken off globally with many countries using selected Japanese brood stock as parent fish. Countries renowned for producing Koi Carp outside of Japan include Israel, USA, Poland, UK, Malaysia and many more. 

As a rule of thumb, Japanese fish often come with the largest price tag. Modern breeders have been operational for many decades and competition is fierce, given the Koi has become an iconic symbol of Japan. With that said some of the aforementioned countries are now also producing exceptional Koi Carp. 


The Types of Koi Carp Explained

There are over 100 variations of Koi Carp and new variations are created on a regular basis, though it is important to note that these may not be recognised at competition level. 

We consider there to be 24 true or regularly witnessed classifications of Koi which we will detail below: 


The Kohaku is a variety of Koi Carp which is largely regarded as the king of Koi, usually fetching the highest prices at the ‘All Japan Koi Show’. The Kohaku, along with the Showa and Sanke make up the Gosanke group (also known as the big three), which are generally the most sought after. The Kohaku is red and white, with a quality fish demonstrating a pure white body with patches of well defined, balanced, primary red colouration which does not extend beyond the eyes or lateral line. 




The Sanke is effectively a Kohaku with black accent markings i.e. the base colour of the fish just like the Kohaku should be pure white, with uniform primary red patches intertwined with smaller amounts of black markings. As with the Kohaku, the markings as a rule of thumb, should not extend beyond the eyes or lateral line. 


The Showa is often confused with the Sanke however there are many signs which differentiate between the two fish. To begin with, unlike the Sanke, the Showa has a dense black base colour which is accentuated with patches of both red and white. The black base colour is of major importance when defining a Showa and unlike Kohaku and Sanke, this often extends beyond the eyes and lateral lines, wrapping around the entire body of the fish. As a final note, Showa’s normally have black colouration on the joint or knuckles of their pectoral fins, sometimes extending out into their entire fin. 

Yamato Nishiki

Yamato Nishiki are metallic versions of the Sanke. Therefore, they are generally coloured in well-defined vibrant, white, red and black, with opaque pectoral fins. These are created by crossing the Sanke with platinum Ogon. 


The Asagi is one of the oldest breeds of Koi going, instantly recognised by its pale blue/indigo back – Asagi is actually the Japanese word for light blue. The back of the fish will have clearly defined scales creating a net-like pattern. At the front of the fish, the head should be cream coloured, and absent of markings, while the belly of the fish below the lateral line should be red or orange. Good examples of Asagi often have lots of colour contrast and are often extremely symmetrical. 


The Shusui is a scaleless (‘doitsu’) version of the Asagi. Shusui don’t have defined net-like scales on their back, and instead are characterised by a single line of large scales along the dorsal line. Just like the Asagi, the head of a great Shusui should be cream coloured and absent of any coloured patterns and the belly of the fish (sometimes extended beyond the lateral line) should be red or orange. 


If you’re looking for a fish with personality, the Chagoi is a great place to start. Chagoi are often described as the friendliest Koi, however this is no more than voracious feeding. The Chagoi has close links to the original Amur Carp and has the appetite to suit – eat to survive. For this reason, the Chagoi will almost always come up for food first and can often be trained to feed from the hand. This often results in a tamer pond, as the other fish learn such feeding habits from the Chagoi. Chagoi are generally brown in colour, though this can vary in shade ranging from almost gold to chocolate brown. 


Soragoi are very similar to Chagoi in personality and can often be a catalyst in taming the fish in your pond to hand feed. This is again due to close links with wild carp which have large appetites. The Soragoi is grey or silver in colour and again can come in varying shades. 


The Ochiba is one of the newer varieties of Koi, and in our opinion less well known. The word Ochiba literally translates as ‘leaves of fall on the water’ which is quite appropriate given the colouration of this fish is generally autumnal grey with patches of brown. The Ochiba was created by crossing Chagoi and Sorogoi, and as a result has an appetite to match. This makes the Ochiba another fantastic fish to assert tamer feeding and even hand feeding. At Complete Koi & Aquatics, we have actually found that the Ochiba are generally tamer than both the Chagoi and Sorogoi making them a fantastic addition to any pond. 


The Bekko is a solid coloured Koi with black spots along the back of the fish. Generally, the Bekko is considered to have a white base coat with black spots, however there are Bekko variations which can have either a red base coat (aka Bekko) or a yellow base coat (Ki Bekko). A good Bekko will have no pigmentation on the head and fins, while the black pattern on the back should resemble small stepping stones and be above the lateral line. 


The Kumonryu is a scaleless (doistu) Koi with a white base coat, intertwined with jet black patterning which often wraps around the body of the fish like a tuxedo. Kumonryu have very unstable colouration which can change from black/white very quickly relevant to changes in temperature, pH, water quality and many other factors. Kumonryu translates literally as ‘nine crested dragon’ which is appropriate for this incredibly striking fish.  


Goshiki were created in the early 1900’s by crossing Asgagi with Kohaku. The end result is a fish, whose name translates literally as ‘five colours’. Goshiki will normally display the colours of a Kohaku (red & white), but with a net like reticulation (typical of the Asagi) existing on the skin surface in black, blue and grey. This makes for an incredibly striking fish which is precisely the negative of a Kohaku. 


Benigoi are Koi with entirely red or orange coloured bodies. Their fins can either be also entirely Red or orange or with white tips. A good Benigoi should have solid and consistent colouration throughout the fish’s body. 


Hariwake are two coloured metallic Koi, consisting of a white skin base colour, overlaid with patches of yellow/orange. The easiest way to spot metallic skin in Koi, is when the pectoral fins are not transparent at the tips. Hariwake are available in both scaled and scaleless (doitsu) varieties. A good Hariwake Koi Carp will have platinum white skin with strong, defined patches of colour. 

 Shiro Utsuri 

Shiro Utsuri OR White Utsuri is a Koi with black skin overlaid with white markings. The word ‘Shiro’ literally translates as ‘white’ in Japanese. On the other hand, Utsuri translates literally as ‘reflections’ in Japanese, and a good fish will display alternating markings similar to that of a chess board. 

 Hi Utsuri 

Hi Utsuri belong to the Utsuri group. The word ‘Hi’ translates as ‘red’ in Japanese, and so Hi Utsuri Koi will be black and red. In keeping with the Utsuri Koi Carp, the patterning along the back of a good Utsuri should be alternating akin to that of a chess board. 

 Kin Ki Utusuri 

Kin Ki Utsuri likewise belong to the Utsuri group. In this case words ‘Kin Ki’ translate as ‘metallic yellow/orange’ in Japanese, and so Kin Ki Utsuri Koi will be orange/yellow and black with metallic skin. In keeping with the Utsuri Koi Carp, the patterning along the back of a good Utsuri should be alternating akin to that of a chess board. In the case of the Kin Ki Utsuri metallic skin can be seen by looking at the pectoral fins which should not be transparent. 


Kikokuryu are metallic versions of Kumonryu Koi Carp. Kikokuryu were created by crossing Kumonryu with Kikusui – the result is a scaleless (doitsu) Koi which demonstrates a white base colour with black tinted scales along the back and patches of black in and around the head, eyes and nose. Kin Kikokuryu are a variation of the Kikokuryu which have the addition of orange/yellow patches.  


Kikusui is the name given to scaleless (doitsu) Hariwake. Therefore, this Koi generally has smooth platinum white skin colouration overlaid with orange/yellow patterning with sharp edges. It is important not to confuse the Kikusui with doitsu Kohaku which will generally have more red markings typical of a Kohaku. 


Goromo are a cross between Kohaku and Asagi Koi carp. The result is a Koi with the stunning white and red patterning of a Kohaku, but as with most Asagi crosses a darker net like reticulation on the skin. In certain instances, this makes the red’s darker, closer to burgundy or even purple. Goromo are very striking Koi Carp and get a lot of attention as they make a fantastic addition to any pond. 


Kujaku are metallic Koi which originate from crossing Goshiki with Matsuba (more specifically Hikarimuji). Kujaku typically have white skin, with a net-like reticulation (similar to that of the Asagi) overlaid with patterns of gold/orange.


Matsuba are Koi Carp which combine a single solid coloured skin with a darker reticulated net like pattern. Matsuba are typically available in white (Gin Matsuba), yellow (Ki Matsuba) or red (Aka Matsuba). 


Purachina (also known as Platinum Ogon) are single coloured, metallic Koi in pure white. A clear and unblemished head, body and fins are key features of a good Purachina. It is common to see Purachina also with reflective (Gin Rin) scales – These are therefore called Gin Rin Purachina. 


Yamabuki, much like the Purachina, is a Koi carp of single, metallic colour but in vivid yellow. As with any single coloured Ogon Koi, it is important that the colour is consistent and unblemished throughout the head, body and fins. Much like the Purachina it is also common to see the Yamabuki with reflective (Gin Rin) scales – These are called Gin Rin Yamabuki. 

 Ghost Koi

Ghost Koi strictly speaking aren’t true Koi, as they are a hybrid between Koi Carp and more naturally coloured wild Carp (common or mirror). The end result is fish which is characterised by many of the traits of true Koi Carp (Nishikigoi) but with dark scales down the back and often dark markings on the face and body. 

In the 1980’s when the Ghost Koi was conceived, they were extremely dull in colouration and as a result were considered to be undesirable. Since then, a combination of time, selective breeding and determination (by countries such as Israel) have yielded beautiful, healthy colourful fish which make a great addition to any pond. 

To summarise this section, as mentioned previously there are many more variations of Koi than we have described and even other hybrids such as Butterfly Koi which have long trailing fins. Not every Koi you will see, fits into a single category and this can make naming them a challenge at times. The most important things to consider when buying Koi is that the fish look healthy, and that you like it – As they say beauty is in the eye of the beholder.  

What is the biggest Koi Carp?

The size of a Koi Carp largely depends on the parent stock but also the diet, weather and water conditions. Typically, in the UK we would expect to see Koi Carp grown on, to get to sizes of 22” – 36”. However, imported fish from warmer countries such as Israel or Japan can be larger with specimens measuring as much as 48” and weighing as much as 90lb. It is often rumoured that they grow larger than Koi Carp, however in our experience that is not the case. They certainly can grow quicker as they are heavy feeders, however overall size will be akin to true Koi Carp and will be largely determined by genetics. 

Are Koi Carp easy to keep? 

Keeping any fish can be as difficult as you make it, and Koi Carp are no exception to the rule. If you stick to the basic principles from the beginning, you can avoid running into any tricky situations and have great levels of success. Feed them, and care for them properly and they will happily grow. 

Top tips for looking after Koi Carp

  1. First and foremost, you are looking after the water and the fish are a bi-product. You are creating a small ecosystem whereby the fish and bacteria in the filter (Nitrobacter and Nitrosomonas) have a symbiotic relationship – the fish produce waste which feeds the bacteria. In turn, the bacteria neutralise the toxins in the waste thereby improving the water quality. 
  2. Test, test and test again. As mentioned above, water quality is king and regular water testing allows you to monitor for any changes, which can (in theory) be corrected. You should have negligible levels of Ammonia and Nitrate. If you are showing signs of either something has gone wrong, and some investigative work will be required. 
  3. Koi Carp are relatively hardy but can naturally struggle with parasitic and bacterial problems. When you are admiring your pond, it is important to analyse the fish – Are they demonstrating any unusual behaviour i.e. not shoaling, not feeding, clamped fins, over-exaggerated breathing. Catching these signs early will allow you to treat for any potential problems before they result in possible fatalities. In these instances, have a skin scrape done on your Koi (which is a microscope level check-up). This can determine whether your pond is harbouring any unwanted parasites. As this does not hurt the fish, we recommend doing this on a regular basis.
  4. Don’t overfeed. The eyes and gasping mouth of a hungry Koi can deceive you into throwing more handfuls of delicious Koi food into the pond. Overfeeding can lead to water quality issues. We recommend feeding no more than twice a day during the summer months, and never once the ambient water temperature drops below 10 °C.

        As with most hobby’s, the more proactive you are, the more success you will have. 

        How long do Koi Carp live?

        Healthy Koi Carp in the UK will typically live 30+ years, so be prepared to commit to the fish. 
        While this is a typical lifespan, they have been known to live much longer - Legendary Japanese fish, Hanako reported lived to the ripe old age of 226. In the unlikely circumstances you happen to be lucky enough to purchase such a hardy fish, be prepared to pass the Koi down to your grandchildren!

        How much are Koi Carp worth?

        Much like anything, Koi carp come in varying shapes, sizes and levels of quality. Bearing this in mind small, single fish start for as little as £3. Over time this fish will grow and change significantly, so to be sure you’re getting the best end-result it is worth spending a little more on small fish. Look out for A grade or handpicked. 
        While shop-bought Koi (4”+) may range from £10 - £1,000 (as a rule of thumb), there are exceptions to the rule. Prize-winning competition fish such as ‘S Legend’ (an All Japan Koi Show prize-winning Kohaku) can sell for as much as £1,400,000. The fish has a length of 101cm which is considered to be large, amongst having an almost perfect body shape and immaculate Kohaku markings of deep red set against pure white. The fish was purchased for breeding purposes and is set to produce over 500,000 eggs. This particular Koi has since died.

        Can you eat Koi Carp?

        In short, Carp are eaten worldwide, and while it is possible to eat Koi Carp, we do NOT recommend it. Koi are considered to be pets, for ornamental ponds and come with an appropriate price tag… This would prove to be a costly meal. 

        How to breed Koi Carp - When do they breed?

        Breeding Koi Carp in the UK can be a challenge as they prefer more high temperate climates for spawning. In order to achieve success, the weather must be appropriately warm. When the time is right (normally in spring/summer), fish will often seek out heavily planted areas of the pond (or spawning brushes where applicable) – Females will scatter eggs and males will follow up by fertilising these. 

        Koi will often consume most of their eggs after spawning. In instances where you have success in breeding Koi Carp, it is good practice to remove the eggs into a separate brooding tank/pond after spawning, or alternatively let nature take its course and hope for survivors.

        What do Koi Carp eat?

        The diet of a Koi Carp changes with the seasons. In the late spring and summer months when the temperature exceeds 16°C, the fish’s digestive system becomes fully active and fish will display voracious behaviour and should be fed a high protein koi stick.  

        In early spring and late autumn typically, when the temperature is between 8-16°C, it is recommended to feed your fish an easy to digest food source such as wheat germ. Wheat germ is high in complex carbohydrates which releases energy much more slowly and is better suited to the fish's slowing metabolism.  

        During winter months or when the temperature is below 10°C, the fish’s digestive system effectively shuts down. Therefore, when this happens, it is recommended to stop feeding your Koi Carp. If Koi sticks are left uneaten, it can negatively affect the water quality, so learn to recognise and understand your Koi’s feeding behaviour. Good quality Koi feed should promote fish health, alongside growth and colour. It will often include vitamins, proteins and carbohydrates which are vital to the fish’s development. 

        Of course, when you are not feeding your Koi Carp, the Koi will naturally graze on delicacies which occur naturally in the pond such as algae, mosquito larvae and flies.  

        Do Koi Carp sleep?

        Koi Carp do not sleep in the same way as mammals. They do not have eyelids to close, and instead go into a catatonic state of deep rest. In order to do this, Koi Carp will generally seek out a quiet, safe spot in the pond, where they will reduce their movements and bodily functions allowing them to re-charge. 

        When Koi Carp sleep, they tend to do this in groups – safety in numbers. This generally tends to be at night, however if there is lots of invertebrate activity after dusk, the Koi may prefer to instead feed. 

        During the winter months, when the temperature drops below 8°C, this will trigger the Koi to reduce their levels of activity going into a rest state of hibernation. Their metabolism slows down and they stop feeding. You will often see the Koi Carp gathering in the deepest areas of the pond, resting on the bottom.  

        Why do Koi Carp jump out of the water?

        When Koi Carp leap out of the water it is generally caused by one of the following reasons:

        • Water quality – When there are significant amounts of Ammonia and/or Nitrites in ponds, Koi will often leap from the water in an attempt to flush toxins from their gills. 
        • Parasites – A Koi with parasites tends to be an itchy, irritable fish. You will often see Koi infected with parasites flashing (scratching) on the bottom of the pond, however on occasion this will cause the fish to leap out of the water. 
        • Spawning – When Koi spawn, they get incredibly excited, chasing females around the pond. Unfortunately, on occasion it is possible for Koi to get too excited and make an exit from the pond.
        • Food – When food is floating on the water surface, excited Koi on occasion will leap from the water as it moves rapidly towards the food. This is often seen when Koi are jumping for flies. 

        How many Koi Carp should I have in my pond?

        The quantity of Koi suitable in a pond, largely depends on the size of your pond but more importantly your filtration system. While some filters state processable feeding rates, it is best to keep an eye on your Ammonia and Nitrite levels. In both cases, these should not exceed 0.2mg/l. If rates are consistently higher than this fish must be removed from the pond, or a larger filtration system must be installed. Overcrowding a pond causes higher nitrite levels, which in turn results in stressed fish with weakened immune systems. The end result of this unfortunately is fish fatalities.

        In fish keeping, you will always have the best levels of success by exhibiting a degree of patience. Add a small amount of fish to begin with in order to let the pond adjust, then add small quantities at a time keeping an eye on water parameters until you are content. Generally, if a pond looks overcrowded, it is. 

        Common problems to overcome with Koi Carp

        The most common problems with Koi Carp generally relates to fish health, however fish health issues tend to be secondary to water quality issues. As mentioned earlier, frequently check your water parameters. We recommend doing these on a monthly basis as a minimum. Check your parameters and make adjustments accordingly. If you do not know how to do this, Complete Koi & Aquatics can carry this out on your behalf, free of charge.

        Why do we do this? Fish can be particularly sensitive to poor water quality. When the fish is exposed to poor water quality and thus elevated levels of Ammonia and Nitrite, the fish becomes stressed. This results in an inefficient immune system making the Koi Carp susceptible to both parasites and then bacteria.

        Most ponds contain low levels of parasites and bacteria at all times. The fish naturally fends these off much like our immune systems routinely defends us against common colds. When the fish is stressed, parasites and bad bacteria will naturally take advantage of the fish's weakened state allowing them to multiply rapidly which can result in issues for other fish in the pond.

        Changes in your fish behaviour can include the following:

        • Clamped fins
        • Repeated flashing (itching, normally on the bottom of the pond)
        • Jumping
        • Gasping for air
        • Lying dormant alone on the bottom of the pond

        In instances where you suspect something is wrong, we recommend bagging up a live fish and bringing it in to Complete Koi & Aquatics for a microscopic scrape. This does not hurt the fish and allows us to establish what is causing the issue so we can treat accordingly.

        There are several common parasites we routinely treat for:

        • The first and most common of these is Costia – a single-cell parasite which attaches itself to the skin/gill membrane and thrives in cold water. In instances where we find Costia, we treat with F-M-G (Formalin & Malachite Green mixture). 

        So, what water quality issues should we be looking out for? Well, all of them… It is vital that all water parameters are in check to improve fish health:

        • The pH should be at a neutral 7.0
        • Ammonia levels should be at 0 mg/L
        • Nitrite levels should be at 0 – 0.5mg/L
        • KH (Carbonate Hardness) and GH (General Hardness) should both be at 120 mg/L

        KH (carbonate hardness) is the pond's buffering capacity for pH. Having a KH at 120mg/L will ensure that the pond remains at a suitable pH (7-8). GH (general hardness) is the levels of Calcium and Magnesium in the pond. Having these at 120 mg/L allows the fish to efficiently perform standard bodily functions such as osmoregulation. Having both GH and KH in check, is also incredibly important for the good bacteria in the filter, which will then better handle the ammonia and nitrite. 

        Please note that organisms in the pond will use these up over the course of the year and these may need topping up subject to additional water tests.

        To conclude, Koi Carp can come against several common issues, however with careful monitoring and proactive management you can prevent unnecessary losses. It is always great practice throughout the year to dose the pond with a combination of good bacteria and enzymes. We highly recommend using the likes of Evolution Aqua Pure Pond / Pond Bombs. These get to work immediately and promote both water clarity and pond health. A single Pure Pond bomb can treat up to 20,000L, there is no risk of over treatment and they are safe for all pond fish.


        To view our range of Koi Carp, visit us in-store or browse and shop online today, with delivery options available between 3-7 days. 

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