Doitsu, Gin Rin, Kin Gin Rin Koi: understanding koi carp scales

People talk a lot about koi colors, much less about their skin. Yet the scale type changes both a fish's appearance, its value and the way it should be cared for. A Doitsu with almost bare skin does not live quite like a fully scaled koi, and a Gin Rin that sparkles in the sun is not judged like a matte fish. Understanding scale types means knowing what makes a koi valuable, while also anticipating its weak points: injuries, healing, sun and parasites.

Wagoi, Doitsu, Kagami: the three scale types

Look at a koi from the side and simply ask yourself: is it covered in scales from head to tail, or is its skin visible? The answer places the fish in one of these families.

In everyday language, "Doitsu" is simply used for all koi with reduced scaling. Among breeders, the type is often specified, because a Doitsu with well-aligned rows and no scattered parasitic scales is worth considerably more than a fish with scales scattered at random. Many varieties exist in both versions: Kohaku and Doitsu Kohaku, Showa and Doitsu Showa, Asagi and its Doitsu version, Shusui.

Origin of Doitsu koi: the introduction of German carp

"Doitsu" is the Japanese transcription of "Deutsch." At the beginning of the 20th century, farmed mirror carp selected in Central Europe for food were introduced to Japan. Their distinctive feature, greatly reduced scaling, was then crossbred with colored carp, giving rise to the first Doitsu koi. Shusui, the Doitsu version of Asagi, is among the oldest varieties to result from this work.

In common carp, the genetics of scaling are relatively well understood: they mainly depend on two genes, whose combinations produce the scaled, mirror, "linear," and leather forms. Some combinations are lethal at the embryonic stage, which partly explains why Doitsu spawns produce varying proportions of each form and why "in-between" fish, such as Yoroi, are found. For the hobbyist, the key point is that scaling is hereditary and fixed from a young age: a Doitsu koi will not become Wagoi, and vice versa.

Gin Rin and Kin Gin Rin: the shining scales

Gin Rin is an entirely different trait. It does not concern the number of scales, but their appearance: some scales contain crystalline deposits that reflect light like glitter. On a white or black area, the shine is silvery (gin); on a red or yellow area, it appears golden (kin). The term Kinginrin encompasses both, and it is often shortened to "Gin Rin."

Several appearances can be distinguished, and their names vary among breeders:

• Flat Gin Rin (beta-gin): the entire surface of the scale shines; the effect is intense but may obscure the pattern.
• "Gin Rin diamond": very vivid faceted reflections, highly sought after in young fish.
• "Gin Rin pearl": scales with a raised, pearlescent center and a softer shine.
• Kado-gin: only the edge of the scales shines, creating a lace-like effect.

Gin Rin can be combined with almost all varieties: Gin Rin Kohaku, Gin Rin Chagoi, Gin Rin Showa… Doitsu koi, on the other hand, have it only on their few scales, which sometimes creates a spectacular effect along the dorsal row.

How to judge the quality of a Gin Rin

A Gin Rin is not judged by the quantity of glitter, but by its arrangement. These are the points we look at, with the fish placed in a clear tank and observed from above and then at an angle:

1. The regularity: bright scales aligned in clean rows, with no gaps or dull areas in the middle.
2. The coverage: several rows on either side of the dorsal line, ideally extending to the flanks.
3. The symmetry: the left and right sides should mirror each other.
4. The luster: a clear, bright shine, not a milky appearance.
5. The pattern: Gin Rin should not overwhelm the colors; a good Gin Rin Kohaku should still be recognizable as Kohaku.

Beware of fish with a few scales that shine randomly: this is not a serious defect, but it is not a Gin Rin that justifies a price premium either. Another point often mentioned by breeders: the luster of certain types of Gin Rin tends to fade with age. If you are buying for the luster, also look at the parents or older fish from the same lineage when possible.

Torn or lifted scales: causes and healing

Two very different situations must be distinguished.

One or a few torn scales: this is mechanical damage. The most frequent causes are overly forceful netting, jumping against a pool edge, a heron attack, rubbing against a rough wall, or agitated spawning behavior. The area appears lighter, sometimes pinkish. In healthy water, the scale regrows within a few weeks. It is often slightly smaller and less regular, and in a Gin Rin, generally lacks luster. This is one reason valuable fish must be handled with great care.

Scales raised across a large part of the body, giving the fish a pinecone-like appearance: this is a serious warning sign, generally associated with a buildup of fluid in the body (dropsy) of infectious or organic origin. Isolate the fish, check the water quality, and seek specialist advice without delay. Our guide on preventing and treating ulcers details the most common skin infections.

To help a wound heal, the basics are always the same: stable, clean water with no ammonia or nitrite spikes, a temperature suited to the fish's activity, and local treatment of the wound when it is open. Products that support the mucus help the skin restore its protective barrier, which is even more useful in Doitsu. Our article on the role of mucus and ImmunoFish care explains this mechanism.

Doitsu and sunburn: should you shade the pond?

Koi naturally live in murky, deep water, where little ultraviolet light penetrates. In a crystal-clear, shallow garden pond exposed to full southern sun, the situation is different. Redness on the back is regularly observed in summer in bare-skinned, white-based fish that spend long hours near the surface. Scaled fish seem less affected, though they are not completely protected.

Should you cover the pond, then? No, but it is wise to offer the fish a choice:

• Sufficient depth: an area at least 1.2 to 1.5 m deep allows koi to descend when it is hot and bright.
• Partial shade: water lilies, shade cloth stretched over part of the pond, a pergola, or a tree at a safe distance. Shading about one-third of the surface is a commonly used guideline.
• Regular observation: if redness appears on a Doitsu's back after a heatwave, increase the shade and monitor how it develops.

Shade has other benefits: it limits water warming, slows algae growth, and reassures fish in the presence of predators. The bare skin of Doitsu also has a practical consequence: visible parasites such as carp lice are easier to spot, allowing you to act sooner. If your fish are rubbing themselves, our article about koi that are rubbing themselves will help you find the cause.

Koi prices and value according to scale patterns

Scale patterns affect a koi's value, but never on their own. General market trends:

For an ornamental pond, scale patterns are mainly a matter of taste. Doitsu are appreciated for the purity of their colors, while Gin Rin are valued for their sparkle in the sun. But remember maintenance: a damaged Gin Rin loses some of its value, and a Doitsu requires a pond with smooth walls, free of sharp edges and cutting stones. Before buying, look at your setup from that perspective.

Read also

A damaged scale is often the gateway for an infection: Koi carp diseases - How to treat them?.

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Frequently asked questions

— What is a Doitsu koi?

It is a koi resulting from crosses with the European mirror carp. It has only a few rows of large scales along the back and sometimes the flanks, or almost none in the forms known as “leather”.

— What is the difference between Gin Rin and Kin Gin Rin?

Both terms refer to reflective scales. Gin (silver) is used on white or black areas and Kin (gold) on red or yellow areas; Kinginrin encompasses both.

— Does a torn-off scale grow back?

Yes, within a few weeks if the water is healthy. The replacement scale is often less regular and, in a Gin Rin, generally does not regain its original shine.

— Can koi get sunburn?

In a shallow, unshaded pond in midsummer, redness on the back is observed, especially in koi with bare skin and light colors. A shaded area and sufficient depth solve the problem.

In summary

• Three main scale patterns: Wagoi (complete scales), Doitsu mirror (rows of large scales) and Doitsu leather (almost bare skin).
• Doitsu descend from crosses with the European mirror carp; scale patterning is hereditary.
• Gin Rin is judged by the regularity, density and symmetry of the reflective scales.
• Scales raised across the entire body: health emergency. A single scale torn off: local care and clean water.
• Bare skin = greater vigilance: partial shade, sufficient depth, gentle handling and parasite control.

Last updated: October 3, 2026.