Complete Guide to Ghost Koi (What Are They?)

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Ghost koi in pond
The ghost koi is not accepted by some koi purists and doesn’t have its own Japanese name. Christine Matthews / CC BY-SA 2.0

Koi come in an incredibly diverse array of patterns and colors. These stunning ornamental fish are prized all around the globe for their peaceful nature, making them perfect additions to garden ponds. With an unmatched value by international standards, koi breeds are some of the most unbelievably costly pets that money can buy. They are true collector’s items, with owners of rare breeds being the envy of seasoned fish enthusiasts.

Considering the historical value given to well-defined patterns and depth of coloration, one might wonder if new, non-Japanese varieties can stand to gain popularity and be sought out in today’s marketplace. Although the Japanese are sticklers for just a handful of critically judged breeds, Western breeders have begun to experiment with hybridizing more strains and creating wholly new varieties. The butterfly koi, a long-finned koi that has sparked controversy, is a variety that has come from this endeavor.

Another modern product of koi hybridization in the West is the ghost koi. This fish doesn’t have its own Japanese name, unlike the breeds that have been selectively bred in the East for centuries. Perception of the value and beauty of ghost koi is largely subjective. Some koi purists and experts consider the hybrid a misfit – practically sacrilegious to have in their ponds – and are reluctant to accept it as an official variety! Others find them just as rewarding to care for and as beautiful as the traditional breeds.

Ghost Koi – A Western Hybrid

Golden ghost koi in pond
Ghost koi have darker markings that give them their “ghost-like” appearance. Matt Buck / CC BY-SA 2.0

Fondly called “ghosties”, ghost koi are a hybrid between Ogon koi and mirror carp. For this reason, many breeders may not consider them true koi despite their being classified as the same species (Cyprinus carpio). They are less domesticated compared to Japanese breeds because mirror carp are a wild mutation of the common carp. Regardless, many fish lovers have grown fond of ghosties due to their interesting patterns and metallic coloration.

The first ghost koi hybrid was created in the 1980s by a British farmer. The wild-sourced mirror carp was dark-colored, resulting in offspring that had the metallic sheen of Ogon koi and uneven black coloration. The exact appearance of the first offspring is unknown, but the resulting strains that arose from subsequent breeding have lighter colored, metallic heads and pectoral fins. The shine from these can be quite exceptional under the moonlight.

The darker markings are instrumental in creating the illusion of these seemingly disappearing “ghost” fish. After subsequent generations, selective breeding has allowed for the production of more strains of ghost koi. There are now varieties with other colors, but the beautiful metallic sheen is maintained. The colors tend to develop and become more vivid, with proper care, as the koi ages.

Some koi retailers and pet shops may refer to evenly white koi or carp as ghost carp just because of their color. These aren’t identical to the variety discussed here. Note that if they are wholly solid-colored and metallic, with distinctly unblemished bodies, the fish may be a Purachina or Platinum Ogon. One of the two primary types of Ogon koi is the parent variety for white ghost koi.  This and more are discussed below.

Ghost Koi Varieties & How to Identify Them 

1) White ghost koi

These come in the traditional koi shape and are also available in the butterfly-finned variety. A hybrid between Purachina Ogon and mirror carp, the white ghost koi has pearly white scales with black markings along its sides and back. The dorsal space in between the eyes is usually free of color. Pectoral fins may or may not have markings.

As this is a fairly new variety, strict specifications on color distribution and pattern requirements are not yet in place. The metallic scales on the head and fins may be silvery in color. There are some specimens that may appear to have the patterns that would typically be seen on an x-ray, except the colors are reversed as the general body tone is white. They look slightly similar to the Japanese Gin Matsuba variety.

2) Yellow ghost koi

This variety looks much like its white counterpart, except its base color is a muted greyish or golden yellow. It is a hybrid between Yamabuki Ogon, which is distinguished by its solid yellow color, and mirror carp.

Scales along the sides and the back tend to be light to dark grey and can look like smudged charcoal. Some specimens may have white-colored scales as well. The pectoral fins may have a gradient of all colors, with rays being distinctly marked. These colors can begin to appear in juvenile koi and tend to be conserved throughout the duration of their lives. Of the highly valued Japanese varieties, yellow ghost koi looks most similar to Ki Matsuba.

3) Butterfly ghost koi

Both yellow and white ghost koi can fall under this category if they have elongated fins. Among the varieties, this one takes the cake for being supported by a niche market. Overzealous koi owners dislike the separate varieties of ghost koi and butterfly koi to begin with, so a combination of the traits would be all the more frowned upon.

Due to the controversies associated with these separate breeds, hybrids between them are likely to be housed in personal ponds and would seldom be seen in competitions or koi conferences.  Nonetheless, those with a general love for ornamental fish would gush at the beauty and gracefulness of butterfly ghost koi.

Keeping Ghost Koi – Health, Growth & Diet

1) Water quality

Ghost koi are able to thrive in garden ponds that maintain high-quality standards for Japanese koi and goldfish. Ideally, the pH should be kept fairly neutral to prevent the fish from developing eye, gill, and skin diseases. Markedly alkaline water may also cause the conversion of waste and elemental compounds into toxic substances. Regularly check the water pH and conduct frequent water changes to maintain optimal levels.

To fully appreciate ghost koi, it would be best to keep the water crystal clear. The fish’s grey coloration and metallic scales would invariably be less appreciated in murky or plankton-rich water. Dissolved oxygen levels should also be maintained at a minimum of 6 – 7 ppm at all times. Apart from keeping the fish calm and comfortable, this would help prevent the buildup of toxic materials.

If you struggle to maintain the water quality of an outdoor pond or are just starting out and getting the hang of pond maintenance, ghost koi are actually a fantastic ornamental fish to start with. Due to their wild heritage, they are more likely to tolerate suboptimal conditions and are generally more resistant to diseases (but may be prone to koi herpesvirus). Moreover, ghost koi have something called ‘hybrid vigor’, which is often seen in mixed breeds that tend to be sturdier and less prone to illness than their purebred ancestors.

2) Temperature

As carp are coldwater fish, it follows that ghost koi are able to tolerate seasonal changes in temperature. The key is to ensure your pond’s depth is at least 3 feet as the koi will simply move toward the pond bottom if ambient temperatures are too cold for them. They should be able to survive outdoors given this depth, even if the surface freezes over. Floating and marginal vegetation should help keep the water cool during summer.

If kept in a tank, the ideal water temperatures for ghost koi range from 18 – 24˚C (64 – 75˚F). Their metabolic capacities are highest at this range. Ghost koi are known for being hardy, so they are more likely to withstand considerable changes in temperature (as opposed to true Nishikigoi). Nonetheless, maintenance of optimal parameters should substantially increase their lifespans.

3) Food

Ghost koi are poikilothermic, just like their predecessors. This means that their metabolic demands change according to water temperature. In spring and summer, their metabolism peaks, and they are able to consume and convert high-protein fish feeds and natural food types into more body mass. As temperatures drop, they are less likely to metabolize proteins and may prefer carbohydrate (wheat-germ) rich feeds. Once water temperatures dip to below 5˚C (41˚F), you should withhold feeding completely.

Ghost koi are omnivorous and may, on occasion, consume pond plants, wild tadpoles, smaller fish, and insect larvae. If they receive ample fish feeds at the right frequency, however, they are less likely to do so. One of the appealing things about koi is they can be interacted with through hand-feeding. Ghost koi are just as likely to take treats from a human hand as fully domesticated varieties.

4) Lifespan and growth rate

When properly cared for, ghost koi live for 20+ years on average. This is typical of many types of carp as they are generally long-lived fish. Ghosties can grow to a considerable length of about 30 inches (76 cm) and more. This variety’s maturation and physical growth rate are similar to that of Japanese koi. They tend to grow larger than cheap, domesticated koi varieties (many of which are the types sold by general pet shops) due to their ancestry.

5) Behavior

Many koi owners share the same apprehensions about ghosties being similar to the more aggressive common carp. Despite their wild heritage, ghost koi are not prone to being aggressive around Japanese koi or other ornamental pond fish. In fact, they are remarkably friendly and peaceful.

Those that are sold in the market are more likely to have been bred using more established ghost koi strains, and not with an authentic Ogon and wild-caught parent. Keep in mind that around 40 years have passed since the first generations were bred, so the ghost koi of today tend to be identical, in terms of behavior, with true Nishikigoi.

While there is hearsay of ghost koi having the tendency to become bullies in ponds, instances of aggression would rarely have anything to do with their heritage. Fish aggression can go well beyond genetics. If you do find that your ghost koi (or any type of koi for that matter) seem to be acting out in an odd way, it’s possible that your pond is too crowded or the water conditions are imbalanced. Keeping a low-density, highly oxygenated pond with compatible fish is extremely important for koi comfort and normal growth.

How to Breed Ghost Koi

Ghost koi are intra-specific hybrids (both parents are varieties of the same species), so they can be bred to produce fertile offspring. Interestingly, these fish are so robust and vigorous that they can rapidly become “invasive” in a small pond. It’s likely that they may also interbreed with other koi varieties. If you would like to prevent this from occurring, you may need to separate males from sexually reproductive females during their gravid period (usually May to June).

In contrast, if you’d like to breed ghost koi, you’ll need to install or create safe areas in the pond for the female to lay her eggs. Floating and submerged vegetation are usually ideal for this. The eggs can be collected after fertilization, which occurs soon after the male koi releases his sperm into the water column. Move the eggs into a small, tightly controlled tank setup that is dedicated to rearing the fingerlings. For more in-depth instructions, browse through our articles on koi “pregnancy” and caring for their young.

Market Value of Ghost Koi & Where to Buy Them

Ghost koi underwater
As ghost koi are not an officially recognized breed, they are usually much cheaper than other koi breeds. Christine Matthews / CC BY-SA 2.0

Because ghost koi are hybrids and are not officially recognized as a legitimate koi breed, they tend to be much cheaper than true Nishikigoi. They are not raised in traditional aquaculture facilities that have specialized in breeding specific, high-value koi strains for dozens of years. Their price usually depends on the conditions in which they were bred, their size and sex, and the visual impact of their colors and patterns.

In the UK, where this variety originates, young ghost koi can go for anywhere between £3 – £20, on average. On the high end, beautifully metallic and large, sexually mature individuals can go for as much as £130. Unlike Japanese koi, their prices seldom go beyond this range.

Ghost koi can be purchased from fish shops, garden centers, and aquascaping stores in the UK. They are not as commonly carried in the US and are not actively traded in the Far East. Online-based retailers that specialize in purebred koi are unlikely to carry them. You may come across individual ghost koi for sale on retail portals like eBay or Amazon, as small-time breeders are more likely to list them there. If you intend to import this variety, make sure to double-check for legal requirements and restrictions in your area.

Chris G
About the author

Chris G

Pond consultant and long-time hobbyist who enjoys writing in his spare time and sharing knowledge with other passionate pond owners. Experienced with pond installation, fish stocking, water quality testing, algae control and the troubleshooting of day-to-day pond related problems.

Read more about Pond Informer.

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