Tategoi: how to spot the potential of a young koi

In a tub of young koi, the eye naturally goes to the most “finished” fish: a crisp pattern, vivid red, and well-placed black. It is rarely the one that will become the most beautiful. A 15- or 20-centimeter koi has shown only a small part of what it will become, and some qualities are revealed only with size and age. A tategoi is precisely that: a young koi chosen not for what it is today, but for what its developing shape, skin, and colors suggest it may become. Learning to recognize them takes time and humility. Here is how to go about it, without fantasizing or being taken in.

Tategoi: what the word means (and what it does not guarantee)

In Japanese breeders' terminology, tategoi refers to a koi kept for further growth because it is believed to have the potential to improve. The term implicitly contrasts with fish said to be “finished,” already at the peak of their beauty, often older, and with pond specimens intended for ornamental use without any particular ambition.

The word is neither a variety nor a certificate. At a dealer's, the “tategoi” label reflects a breeder's or seller's opinion, nothing more. That opinion may be highly informed when it comes from someone who knows the parent line and has watched hundreds of fish from the same parents develop. It may also be nothing more than a sales pitch stuck on a tub of tosai (one-year-old koi) to justify a price.

So remember two things. First, a tategoi is a gamble, and every gamble has losers. Second, potential can only be realised if the living conditions are right: water volume, water quality, feeding, temperature and freedom from stress. An excellent young fish in a pond that is too small and poorly filtered will never become what it promised to be.

Tategoi generally refers to fish between one and three years old: tosai, nisai (two years old), and sometimes sansai (three years old). The younger the koi, the more uncertain the gamble and the lower the price. The older it is, the clearer the picture becomes, and the more you pay for that clarity.

Shape first: the skeleton does not lie

The colours change, the pattern shifts, and the skin becomes finer or duller. The bone structure, however, is already set. This is why connoisseurs look at the silhouette before anything else, and it is also the most accessible criterion for an attentive amateur.

Observe the fish from above, in a blue or white basin, with calm, shallow water. You are looking for:

• A perfectly straight spine, without a slight “S” shape, hump or hollow along the back.
• Broad shoulders just behind the head, giving the body strength. In a young fish, this volume is more suggested than visible.
• Left-right symmetry: the body should not be more rounded on one side.
• A well-proportioned head, neither too small (the fish will look “pointed” as an adult), nor too elongated.
• A thick caudal peduncle, the part that connects the body to the caudal fin. A thin peduncle often produces an adult lacking presence.
• Balanced-sized pectoral fins, symmetrical and well spread.

Next, look at the fish from the side as it passes close to the wall. A harmonious back line that rises gently behind the head and then slopes regularly down towards the tail indicates an elegant adult. A broken line, or a belly that sits very low compared with the back, will not improve with age.

A word about sex. At the same size, females generally develop more volume and reach larger adult sizes, which explains why the majority of large, prize-winning specimens are female. With a tosai, visual sexing remains uncertain. A slightly broader body, rather rounded and less massive pectoral fins are clues, not proof.

The skin: the white base and the depth of the hi

After body shape, skin quality is the second major criterion, and the most difficult to assess from a photo. You need to see the fish in person, under natural light, ideally at different times of day.

Shiroji, the white base. In Kohaku, Sanke, and Showa, white forms the background of the pattern. Good white is dense and luminous, with no yellowish cast or translucent, “waxy” appearance. In a young fish, slightly creamy white may brighten in good-quality water; however, stained white, white speckled with red spots, or dull white does not bode well. White that allows the pink of the flesh to show through, particularly around the head, is a common defect in very young fish and does not always disappear.

Hi, the red. The red of a koi is not simply a color: it is a more or less thick layer of pigment. In a young fish with strong potential, the hi may appear orange, almost matte, but it is dense and even across the entire plate, with no faded areas. As the fish grows, this type of hi tends to deepen. Conversely, a very vivid but thin red, through which the scales show as if beneath a veil, may fade or break up with age.

Lustre. The skin of a good koi looks lively, almost lacquered. This is partly genetic and partly related to health and diet. A young fish with dull lustre in clean water is a warning sign.

The pattern edges. Kiwa is the rear edge of a red plate, where the red meets the white. In a high-quality adult, it is crisp and follows the contours of the scales. Sashi is the front edge, where the red extends beneath the white scales and appears blurred. In a young fish, a fairly wide sashi is normal and often tightens as the fish grows. A kiwa that is already crisp is a good sign; a blurry kiwa is a question mark.

Rising sumi: reading the black hidden beneath the skin

Black, or sumi, is the most unpredictable color. In Sanke and especially Showa, much of the black is not yet visible in a young fish. It lies deep beneath the skin and gradually rises toward the surface over the months and years. This is known as sumi “rising.”

In practical terms, look at the areas of the body that appear gray, bluish, or slate-colored, like a shadow beneath the white. These areas are often the future black. A very “gray” young Showa can thus become, two or three years later, a fish with powerful, well-structured black. Conversely, a young fish whose black has already fully emerged and is highly contrasted is sometimes a fish that has already reached its maximum, and whose black may spread in a disordered manner.

A few useful guidelines:

• Quality sumi is dense and glossy, like lacquer, not brownish or faded.
• In Sanke, crisp black patches set on the white and red are preferred, mainly on the front half of the body, without spreading over the head.
• In Showa, the black wraps around the body and enters the head; a young fish with lots of well-distributed gray is often a good bet.
• Black reacts to its environment: it is common to observe it fading in warm water and deepening in cooler water, while very soft water makes it less intense. So do not judge sumi based on a single observation.

The most common mistake is choosing the young fish whose black is already “finished” at 15 cm: it looks impressive in the bowl, but rarely has much room for improvement.

Variety by variety: what to look for

The general criteria apply to all varieties, but each variety has its own signs. The table below summarizes the points that deserve your attention in a young fish.

The motoguro mentioned for Showa refers to the black at the base of the pectoral fins. It is a sought-after trait in this variety, and its early presence in a young fish is a rather good sign.

The classic pitfalls when buying a tategoi

The young koi market is broad and uneven. A few mistakes keep coming up, even among already experienced hobbyists.

Choosing based on a photo. A well-lit photo taken in a blue tub makes almost every fish look better. It shows neither how the fish swims, nor its true luster, nor the depth of the hi. If you buy remotely, ask for a short video in natural light and several views.

Confusing “pretty” with “promising.” A highly colorful young fish with a complete pattern is attractive. But it is often a fish that has already revealed most of what it has to offer. A tategoi is often a somewhat “unfinished” fish, paler, with a pattern that is still changing.

Ignoring physical defects. A shortened operculum (the gill cover does not completely cover the gills), a crooked mouth, a missing or deformed fin, a cloudy eye, a slightly curved spine: these defects do not disappear. A show fish cannot have them, and even a pond fish may sometimes suffer from them.

Neglecting health. A young fish that rubs itself, stays apart, has clamped fins, or breathes rapidly is a risk to your entire pond. Whatever its potential, several weeks of quarantine remain essential before introducing it.

Paying for a bloodline without verifying it. The name of a reputable Japanese breeder is a reference point, not a guarantee. The same cross produces thousands of young fish, of which only a small fraction will become exceptional. A good seller will honestly tell you what they think of each fish, including its flaws.

To get an idea of the price differences and what justifies them, also see our article on the value of the koi in your pond.

Raising a tategoi: what depends on you

The best fish in the world only reveals its potential in an environment that allows it to thrive. Japanese breeders raise their promising young fish in mud ponds during the warm season precisely because the space, natural food, and stability there encourage rapid, harmonious growth. In a garden pond, you can come close to providing those conditions.

Water volume. A koi grows better, and more evenly, in a large, lightly stocked volume. The more fish there are per cubic meter, the more each fish's growth slows. If you are aiming for large koi, limit the population rather than multiplying your purchases.

Water quality. Ammonia and nitrites at zero, nitrates under control, stable pH, sufficient carbonate hardness, and abundant oxygen. Impeccable water maintains a clean white and a vivid luster. Unstable parameters do the opposite.

Temperature and the growing season. Growth is strongest between spring and the end of summer, when the water remains consistently above around twenty degrees. In Belgium, this window is short: this is the time to feed generously, with quality food divided into several meals, provided the filtration can keep up. To learn more, read our tips for successful koi growth.

Feeding. A feed rich in high-quality protein during the peak season, a more digestible feed when the water cools, and color-enhancing food used in moderation. Excessively pigment-rich food can slightly tint the white. Our guidelines are detailed in the guide to choosing good food for koi.

Photographic tracking. This is the most underestimated tool. Photograph each young fish from above, in the same tank, at the same time and under the same light, in spring and autumn. Record its size. After two or three seasons, you will know which ones are progressing, which are stagnating, and above all, you will have trained your eye better than with any book.

Realistic expectations: the gamble and the timeline

A hobbyist who buys a tategoi must accept a degree of uncertainty. Even the best breeders are regularly wrong, and that is precisely why young fish cost less than fully developed adults.

A sensible strategy is to buy several young fish of medium to good quality rather than a single very expensive one, then observe them. After two seasons, some will have progressed and others will not. The latter remain beautiful pond fish; the former become the pride of your collection.

As for timing, most varieties show the bulk of their potential between three and five years. Some, such as Showa or Sanke with strong sumi, may continue to develop beyond that. The hi of a high-quality Kohaku often reaches its peak around five or six years of age before slowly refining. These are broad guidelines: every fish follows its own rhythm, and so does every pond.

One final point: a tategoi is a promise of beauty, not a financial investment. Few hobbyists resell their koi, and fish that genuinely increase in value are rare. Buy for the pleasure of watching a fish transform, not to make a profit.

Common case: choosing between two young fish in the same bowl

Typical situation: two Kohaku of the same size. The first has bright red, a complete pattern from nose to tail, and a decent shape. The second is paler, its red leans toward orange, and its pattern is a little short, but its body is broad and even, its white is impeccable, and its hi is perfectly uniform.

Most beginners choose the first. An experienced breeder will very often choose the second: superior shape, better-quality skin, and dense red that has every chance of deepening. The pattern itself shifts as the fish grows, and its relative length changes. If you are hesitating, ask the seller to place both fish side by side in a blue bowl and take the time to watch them swim for a few minutes.

Another common case: a very gray young Showa next to a Showa that already has strong contrast. The first may look dull, but if the gray is evenly distributed and the shape is good, it is often the one that will develop the most beautiful black in three years. The second is immediately attractive, with the risk that its black will continue to spread and blur the pattern.

Also read

Before investing in a promising young fish: How to estimate the price of a koi carp?.

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Frequently asked questions

— What exactly is a tategoi?

It is a young koi, generally one to three years old, that is selected and raised because it is considered likely to become more beautiful than it is today. It is neither a variety nor a guarantee, but a breeder’s or seller’s assessment of its potential.

— Which criterion should you look at first in a young koi?

Body shape. The spine, shoulder width, symmetry, and thickness of the caudal peduncle will not change, whereas colors and pattern continue to develop as the fish grows.

— What does “sumi rising” mean?

In Sanke and especially Showa, some of the black is still deep within the young fish. It appears as gray or bluish areas under the skin and gradually rises toward the surface over the seasons.

— At what age can you tell whether a tategoi has lived up to its promise?

Generally between three and five years, depending on the variety and rearing conditions. Some koi with strong sumi continue to develop for longer. Regular photographic monitoring makes it possible to observe this objectively.

In summary

• A tategoi is a bet on the future of a young koi, not a guarantee.
• Body shape comes first: it is already written in the skeleton.
• Dense hi, even when orange, and bright white are better than vivid but thin red.
• Gray areas under the skin of Sanke and Showa often indicate future sumi.
• Water volume, water quality, growing season, and feeding determine the outcome.
• Photograph your young koi each season under the same conditions to assess their development.

Last updated: October 3, 2026.