Quick Answer
Shusui is the scaleless (Doitsu) counterpart to Asagi — a blue-grey koi with a single row of large mirror scales along its back instead of full scaling, with red (hi) or yellow (ki) markings along its sides. It was the first Doitsu koi variety ever bred, created in the early 1900s by crossing an Asagi with a scaleless German carp. The name “Shusui” (秋水) translates to roughly “autumn water.”
What Is Shusui Koi?
Shusui is essentially Doitsu (scaleless) Asagi — the same blue-grey coloration and red or yellow markings, but with a mostly scaleless body and a single row of large, mirror-like scales running along the dorsal line instead of full body scaling. That exposed, streamlined look is what sets it apart from every other blue koi variety: Asagi and Shusui are the only two koi varieties that carry true blue coloration.
Origins and History
Shusui was created in the early 1900s — commonly dated to around 1910 — by a breeder generally credited as Akiyama, who crossed an Asagi with a scaleless German carp (sometimes called mirror carp, imported to Japan for food production) to produce the very first Doitsu koi variety. Nearly every modern koi variety today carries some Doitsu bloodline, so Shusui holds a genuinely foundational place in koi breeding history, even beyond its own popularity.
As with most koi origin stories, exact names and dates vary across sources — some cite 1908, others 1910 or later — so treat the specifics as the hobby’s standard account rather than a documented historical record.
How to Judge Shusui: Scale Row, Head, and Color
Because Shusui exposes so much of its body, flaws that would be hidden under full scaling are immediately visible. A few specific traits matter most:
- Scale row symmetry — the single row of mirror scales along the dorsal line should be even, straight, and unbroken on both sides. Missing, doubled, or out-of-line scales are the most common fault judges look for.
- Head clarity — as with Asagi, a clean, unmarked head is essential, though Shusui’s head doesn’t need to be as pure white as an Asagi’s.
- Color stability in hard water — Shusui’s blue mirror scales can shift toward grey or black in hard water conditions, and once that shift happens, it doesn’t reverse. Water hardness is worth checking if a Shusui’s blue looks duller than expected.
- Hi/Ki distribution — red or yellow markings should be clean and well-placed along the sides, with a crisp boundary rather than a blurred one.
Shusui Color and Pattern Varieties
Shusui comes in a handful of recognized color and pattern variations:
Standard (Blue) Shusui has the classic blue-grey mirror-scale back with red markings along the lateral line and head. This is the baseline form the other variations build on.
Hi Shusui carries red (hi) extending up over the back rather than staying confined to the sides, so the contrast is between the red and the dark blue of the mirror scales rather than red against a paler ground.
Ki Shusui (also called Yellow Shusui) follows the same pattern logic as Hi Shusui, but with yellow (ki) in place of red. Classification here can get blurry — if there’s no blue ground at all and the back scales read as black rather than blue, some judges would place the fish as Ki Matsuba Doitsu instead of true Ki Shusui.
Red Shusui shows intense, extensive red markings running from head to tail against the blue mirror-scale back.
White Shusui has a predominantly white ground rather than blue, with the mirror-scale row and red or yellow markings still present as accents.
Pattern Variations
Hana Shusui (“flower” Shusui) refers to Shusui with a particularly striking, floral-looking distribution of hi against the mirror-scale ground — the pattern reads as scattered blossoms rather than solid bands.
Butterfly Shusui is a hybrid cross between Shusui and long-finned Butterfly (Nagoya) koi — a hobbyist favorite rather than a formally recognized show variety, valued for the flowing fins layered over Shusui’s coloration.
Since Shusui already is Doitsu Asagi by definition, you’ll sometimes see fish marketed as “Asagi Shusui” or “Doitsu Shusui” — in practice these names are just emphasizing the Asagi-pattern lineage or the scaleless trait that’s already inherent to the variety, rather than naming a distinct sub-type.
Shusui Koi Care Guide
Shusui don’t need meaningfully different care from other koi. A pond with a minimum depth of three to four feet, solid filtration, and good aeration covers the basics. Test water regularly for pH, ammonia, nitrite, and nitrate, and perform routine water changes to keep the pond clean and stable — water hardness is worth monitoring specifically for Shusui, given its effect on scale color discussed above.
Feed a high-quality koi pellet as the base diet, in small, frequent portions rather than one large feeding, and reduce or stop feeding in winter as the fish’s metabolism slows. Quarantine new fish before introducing them to an existing pond to protect against disease.
Shusui Koi Breeding
Breeding pairs are typically selected for coloration, scale-row quality, and conformation. Spawning is generally induced by gradually raising water temperature and providing spawning substrate for the adhesive eggs. Fry need close monitoring and a high-protein diet early on, with careful culling as they mature — not every fry will show the scale-row precision or clean coloration needed to meet breeding standards, so selective culling is part of maintaining quality bloodlines.
Shusui in Japanese Culture
Koi broadly symbolize perseverance and good fortune in Japanese culture, often depicted swimming upstream against a current as a symbol of overcoming obstacles. As one of the oldest Doitsu varieties, Shusui carries an added layer of historical significance in koi breeding — nearly every modern koi variety traces some lineage back to the Doitsu bloodline Shusui helped establish.
Conclusion
Shusui rewards the same eye you’d bring to Asagi — head clarity, clean color distribution — but adds one more thing to check: the mirror-scale row itself, since there’s no full scaling to hide an uneven one. If you’re comparing Shusui to other blue koi, remember there really isn’t much competition — Asagi and Shusui are the only two koi varieties with true blue coloration.
Frequently Asked Questions (FAQs)
What does Shusui koi mean?
“Shusui” (秋水) translates from Japanese to roughly “autumn water,” a reference to the fish’s blue-grey mirror-scale coloring.
What is a Hana Shusui koi?
Hana Shusui (“flower” Shusui) is a Shusui with a particularly striking, scattered distribution of hi (red) against the mirror-scale ground, giving the pattern a floral appearance rather than solid bands.
What are the different types of Shusui?
The main recognized variations are Standard (Blue) Shusui, Hi Shusui (red extending over the back), and Ki Shusui (the same pattern in yellow). Hobbyist and market terms like Hana Shusui, Butterfly Shusui, and “Doitsu/Asagi Shusui” describe pattern or hybrid variations rather than separate formally judged categories.
Why did my Shusui’s blue color turn grey or black?
This is typically caused by hard water — Shusui’s mirror scales can shift from blue toward grey or black under harder water conditions, and once the shift happens, it generally doesn’t reverse. Checking and adjusting water hardness is worth doing if you notice this early.
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Passionate about fish keeping since elementary school in the 1980s, Giovanni Carlo has dedicated countless hours to collecting and breeding a diverse array of ornamental freshwater fish. From vibrant guppies and majestic koi to striking bettas and classic goldfish, he continues to explore the fascinating world of aquatics, sharing knowledge and enthusiasm with fellow fish enthusiasts.