Doitsu Koi Scaleless Variety Guide: Mirror and Leather

Doitsu koi trace their smooth skin to a turn-of-the-century cross between Japanese carp and European table fish, and the result still divides collectors more than a century later. This doitsu koi scaleless variety guide explains the difference between mirror and leather forms, what judges penalise in the dorsal scale line, and how the reduced scale protection changes day-to-day husbandry in a tropical pond. The notes below come from Gensou Aquascaping in Singapore, drawing on years of keeping doitsu Sanke and Kumonryu alongside fully scaled koi.

Quick Facts

• Origin: German mirror carp (Doitsugoi) crossed into Japanese koi lines from 1904
• Two forms: Kagami-goi (mirror) and Kawa-goi (leather)
• Applicable across varieties: Doitsu Kohaku, Sanke, Showa, Kumonryu
• Pond size: 5,000 litres minimum, gentle surfaces essential
• Water temperature: 20-28 degC in Singapore outdoor ponds
• Skin sensitivity: higher abrasion and sunburn risk than scaled koi
• Judging: matched dorsal scales, no random scattered scales on flanks

German Ancestry and Japanese Refinement

In the early 1900s Japanese breeders imported Doitsugoi — scale-reduced German carp originally farmed for easy filleting — and crossed them into nishikigoi lines. The modern doitsu koi keeps that scale pattern as a recessive trait, producing fish with two neat rows of enlarged scales along the dorsal line and otherwise bare skin.

Purists argue that doitsu lack the depth of colour possible under a wagoi scale grid. In reality, good doitsu show hi and sumi with almost lacquered clarity precisely because no scale edges break up the pigment.

Mirror Versus Leather

Kagami-goi, the mirror form, carries a row of large reflective scales running each side of the dorsal fin, with occasional scales along the lateral line. Kawa-goi, the leather form, is almost entirely bare — only a few dorsal scales near the head remain, giving a soft suede appearance.

Leather doitsu are rarer and more expensive but also more fragile. Mirror doitsu with clean twin dorsal rows are the commercial standard and what most Singapore importers bring in under the Matsunosuke or Marusei names.

Judging the Scale Pattern

Judges want symmetry. Both dorsal rows should have similar scale counts, with each scale sitting flat against the skin, evenly spaced and aligned. Scattered scales on the flanks, missing scales creating gaps, or enlarged “headlight” scales near the shoulders all pull scores down.

Colour judging follows the fish’s base variety. A Doitsu Sanke, for instance, is judged on hi and sumi placement exactly as a scaled Sanke would be, with a bonus for skin that shows pigment with glass-clear edges.

Popular Doitsu Varieties

Doitsu Kumonryu is among the most dramatic — a black-and-white pattern that shifts seasonally with water temperature. Doitsu Sanke shows classic red, white and black with unusually crisp edges. Doitsu Showa, sometimes called Kage Showa when the sumi bleeds, is technically demanding to judge because black often sits deeper under the skin.

Beni Kikokuryu and Kikusui are metallic doitsu varieties that have become very popular with Singapore keepers over the last decade for their reflective quality under landscape lighting.

Husbandry Differences

Scaleless skin loses its protective mucus layer faster. Smooth pond surfaces matter: pebbled render, rough quartzite edges and exposed bolts cause scrapes that scaled fish would shrug off. Seal all internal surfaces with pond-grade epoxy, and round every corner.

Tropical sun is also harsher on bare skin. Provide at least 40 percent surface shade, whether from lily pads, a pergola or sail cloth. Without it, doitsu develop dull grey-brown patches on exposed flanks within months.

Water Parameters in Singapore

Target pH 7.2-7.8 with KH above 5 to prevent the acid swings PUB water can cause after heavy rainfall dilutes pond alkalinity. Chloramine must be neutralised fully before any water change — doitsu show chemical burn damage faster than scaled koi because there is no scale barrier.

Keep ammonia and nitrite at zero through a multi-stage mechanical and biological filter sized to at least one turnover per hour. A 20-watt UV clarifier helps control the green water bloom typical of exposed tropical ponds from March onwards.

Feeding and Growth

Doitsu often grow faster than scaled koi, reaching 60 cm by age three under good conditions. Feed a balanced 35-40 percent protein growth pellet at 2-3 percent body weight when water is above 22 degC. Colour-enhancing pellets work well on doitsu because there are no scale edges to mottle the pigment.

Buying in Singapore

Expect $300-$600 for tosai doitsu with decent pattern, and $2,000+ for nisai-plus fish with papered bloodlines. Reputable dealers around Pasir Ris Farmway and Serangoon North stock doitsu regularly, and specialist importers run auctions for show-quality fish several times a year.

Related Reading

Kohaku Koi Variety Care Guide
Sanke Koi Variety Care Guide
Showa Koi Variety Care Guide
Asagi Koi Care Guide
Koi Fish Care Guide Singapore