When do Koi Fry get their Color? (Color Development Guide)


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Guide to Koi Fry Color Development – When do Koi Fry Get their Color?

Three koi with different coloration & patterns swimming together
Koi coloration can determine the rarity, value, popularity, and general appeal of the fish, making it a very serious topic for professional breeders and avid collectors. Bernard Spragg. NZ / No copyright

With the potential to develop a whole array of stunning colors and patterns, koi are one of the most popular ornamental fish species. Koi coloration is quite a serious topic to broach with professional breeders and avid collectors. It can determine the rarity, value, popularity, and general appeal of the fish. Even the depth and transparency of color, its solidity in distinct shapes, and the presence of a gradient all add up to a score when breeders select for desirable traits in parent fish.

Originating from wild carp, koi have been selectively bred for centuries. The first-ever “koi” kept in an ornamental pond likely had dull colors that were a far cry from those that are considered fairly common nowadays. Breeders in the Far East persevered, cultivating generation upon generation of koi until they were beautiful enough to be a central attraction in the properties of royal families.

With advances in koi breeding and cultivation, the challenge today lies in enhancing the quality of fish to create robust individuals with colors that last a lifetime. Though a measure of color predictability does exist, an element of surprise always remains as these living jewels aren’t born with their colors!


Do All Baby Koi Look Alike?

A baby koi with orange coloration
After a few weeks, koi hatchlings may begin to show their first colors and patterns but there’s no guarantee that they’ll stay that way. Image by Giovanni Bagayas from Pixabay

Koi hatchlings, or koi fry, look like miniature versions of their parents, but only in form. Even the most colorful and vivid koi will produce eggs that hatch into dull-colored fry. This likely serves as a survival advantage, as predators are less likely to spot plain-colored fish.

Healthy koi eggs will have a yellow-ish color and have little eyes begin to develop after a few days.

During the first few days to weeks of life, breeders will select koi hatchlings that exhibit a healthy rate of growth and development. Some hatchlings may begin to show their first colors and patterns after a few weeks, but these are likely to change. Rearing baby koi is always an exciting experience as it can be fun to predict how they’ll look as adults. Nonetheless, health takes precedence over color and pattern, especially at this point in a koi’s life.


When Do Koi Fry Get Permanent Color?

An adult koi swimming alongside a young koi
Young koi will begin to show more distinct patterns after about 1 – 2 months of growth. randychiu / CC BY 2.0

The healthiest koi fry may be selected and separated according to color in as early as 4 – 6 weeks. After about a month or two of growth, young koi will begin to show more distinct patterns. Don’t get excited just yet, however, as these first colors may either fade completely or change into other combinations! The rate of development and exact period of color permanence largely varies, with some koi exhibiting subtle changes in color all throughout their lives.

You’ll find that many seasoned and highly respected breeders in Japan begin to sell top-quality koi after at least two years past the hatching date. It would be difficult to place a fair value on younger koi, with colors and patterns that have yet to approach permanence. The rapid size increase at the juvenile stage inevitably changes how a color pattern is oriented throughout the full body. To ensure that they obtain fish with mature coloration, collectors may opt to purchase koi that are at least 3 – 4 years old. Furthermore, there are many factors apart from age that affect color intensity.


Factors That Affect Color Development

1) Genetics

A Kohaku koi next to a Showa koi
Purebred koi, who come from well-established bloodlines, tend to have more vivid & desirable colors. Notable bloodlines include Kohaku and Showa (pictured). randychiu / CC BY 2.0

Just as our genes determine our most distinct features, koi genetics plays the most important role in determining color. Purebred koi, arising from well-established bloodlines, tend to have the most vivid and desirable colors. Hybrids or fish that are a result of accidental breeding may develop less distinct colors and patterns.

Japanese koi breeders usually specialize in specific bloodlines, in pursuit of increasingly rare patterns. The most notable bloodlines are Kohaku, Sanke, Showa, and Ogon. The DNA sequences of each of these types have been thoroughly studied for mutations. It turns out that just a handful of minor changes in the DNA baseline can reliably distinguish strains from one another. These result in various color phenotypes – the physical expressions of either dominant or recessive genes.

To achieve their goals of breeding fish with unique colors, breeders must be critical about their choice of parent fish. Some colors are more dominant in the gene pool than others. If they wish to increase their chances of having purely red and white koi, they must select a male and female that have directly descended from pure Kohaku bloodlines. The process is quite complex and does result in many young fish that simply do not meet the mark.


2) Food

Koi eating fish food in a pond
Koi food can greatly affect koi pigmentation. When possible, use top-quality feed mixes that contain spirulina or carotene. Image by Karl-Heinz Schäfer from Pixabay

Koi food can act as a vital color enhancer, causing pigments to deepen over time. Top-quality koi feed mixes are designed with color development in mind. A shift to a low-quality feed can quickly result in the lightening of a few pigments as some nutrients and vitamins are lost. This explains why newly imported koi may be remarkably vibrant in color, only to appear faded after a few months of growth in the hands of a new owner that skimps on food.

Carotene and spirulina are some natural ingredients to look out for in quality food. These aid in color development as they provide pigment compounds for skin cells. Don’t expect koi color to brighten overnight, however! It can take years for skin pigments to build on one another to create a truly deep shade. Think of koi color enhancement as the process behind creating a classical oil painting. Layers of highly pigmented cells, like layers of paint, take time and energy to produce.

Color-enhancing food shouldn’t simply be fed in abundance throughout the year, either. They are most effective during the koi’s rapid growth period (likely July to August). Outside of this window, koi cells tend to slow in growth and division. A high quantity of enhancers can cause discoloration instead! Note that the koi diet should be altered according to their growth cycle, which is influenced by seasonal temperature variation.


3) Temperature

Group of koi swimming in a pond in the fall
Koi colors tend to deepen in late fall and winter as their metabolism slows down & pigment accumulates in their cells. Peter Stevens / CC BY 2.0

Japanese breeders prefer to hold their koi shows in late fall or winter as this is when koi colors tend to deepen. This is possibly due to slowed metabolism and increased accumulation of pigments in cells. As koi stop eating and temperatures drop, their skin cells may experience a lengthier turnover rate. Conversely, during the peak growth period in summer, koi colors may fade.


4) Quality of care

Koi swimming in a slightly dirty pond
If koi are in a pond with poor water quality, low oxygen levels, or pathogens, they may be under stress and as a result, have a duller complexion. Kamillo Kluth / CC BY 2.0

Fish that are subjected to stress are less likely to develop vibrant colors. Stress can also cause rapid color loss. Poor water quality, the presence of pathogens and predators, and low oxygen concentrations can delay proper color development in young koi.

The outer appearance of koi says a lot about their internal state. Just as an unhealthy pallor can indicate sickness in humans, a faded complexion can indicate that your koi is sick. This will usually be accompanied by other behavioral indications of stress. Make sure to keep a close eye on koi that seem to be losing their colors.

When cared for properly, healthy koi can appear to glow as their colors deepen. This is most evident in strains that have dark-colored patterns on a white base. The contrast between the light and dark colors intensifies until the pattern mimics the appearance of ink on paper.


Does Pond Color Influence Pigmentation?

A Shusui koi
If you’re taking pictures of koi then a blue tank can help to make their pigmentation look more vivid, though it may be less noticeable with Asagi and Shusui koi (pictured) because they have blue pigmentation. KoiQuestion / CC BY-SA 2.0

Many wild aquatic animals develop colors that blend in with their environment. This is a survival strategy that helps keep them masked from predators. As koi have been fully domesticated, they don’t necessarily develop colors that help camouflage them. The jury’s still out on how significantly tank color can affect koi pigmentation, although one study has shown that it can influence the skin color of common carp. A dark pond color may certainly give the illusion of deepened pigmentation.

Another tank color that koi enthusiasts might be curious about is blue. Koi owners always opt to showcase and photograph their koi in bright blue tanks. This doesn’t cause any real changes in color, but it does “enhance” the vividness of pigments as light bounces off of the tank and onto the scales. Blue pigmentation (mostly found in Asagi and Shusui types) is also seldom produced by koi, so they won’t blend in with this background.


Koi Chromatophores: Color-Producing Skin Cells

Squid chromatophores
Chromatophores are specialized epithelial cells that can reflect and refract colors, determining koi coloration. Minette from Seattle, Washington, CC BY 2.0, via Wikimedia Commons

Skin coloration in koi is caused by pigments in chromatophores, which are specialized epithelial cells. Chromatophores are able to reflect and refract colors, determining which ones are visible to us. They contain three types of pigments: carotenoids, which produce an array of reds to yellows; melanins, which are responsible for brown and black; and purines, which produce iridescent coloration. Among these three, only carotenoids need to be supplemented in the koi diet as they are unable to produce this on their own.

Chromatophores take time to fully develop and are subject to the availability of nutrients and overall fish health. Like our own skin cells, these undergo cell division and continuously become replaced. Thus, maintenance of koi coloration is a lifelong endeavor. Intensification of color can occur when pigments increase in concentration, the number of chromatophores increases, or pigments migrate into deeper cell layers.

Unfortunately, koi can also lose their colors due to environmental and physiological stresses. Even mild pond additives that cause water parameters to fluctuate can result in color loss. In some cases, fading may be irreversible. Nonetheless, koi at their peak growth period may still recover and produce intensified pigments after a few months of rehabilitation. If you notice losses of color that occur in more than just one fish you will have to go through your maintenance checklist.


Color Development in Hybrid Fry

Large group of Shiro Utsuri koi in a tank
Koi hybridization has helped shed light on the dominance of certain color phenotypes and patterns. Black patches, for example, are actually caused by a mutant gene! KoiQuestion / CC BY-SA 2.0

Hybridization is a great way to mix and match the color traits of Japanese koi bloodlines. It also adds an element of excitement and unpredictability! Will offspring have a perfect mix of colors from both parents, or will the traits of one be favored?

Hybridization has shed light on the dominance of certain color phenotypes and patterns. The gene that codes for orange pigments appear to be more dominant. Blue, white, and grey coloration may depend on the presence of recessive genes. The Kohaku koi, known for its orange-red pattern on a stark white background, comes from a purebred stock that dates back to the late 1800s. It was one of the first well-established ornamental breeds that could produce offspring with color combinations that were consistently comparable to those of their parents.

Interestingly, the occurrence of black patches, now desirable in Showa, Sanke, and Bekko koi, is the result of a mutant gene. Hatchlings that are born with this mutation don’t develop their first black spots until they are at least 2 weeks old. Evidently, though color development is inherently coded in koi DNA, it needs to be approached with due patience!

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