Japanese koi are bred across Japan, with the highest concentration of elite breeders located in Niigata — the birthplace of koi keeping. These master breeders have refined bloodlines over generations, focusing on ideal body conformation, vibrant skin quality, and well-balanced patterns that meet strict Japanese standards. Unlike mass-produced domestic koi, Japanese farms often specialize in specific varieties and raise each fish with individual attention. The result is koi that are appreciated worldwide as living art — a reflection of tradition, precision, and beauty.

Domestic koi — whether bred in the U.S. or imported from lower-cost sources — are typically produced in large volumes with less focus on refinement or lineage. Japanese koi, by contrast, are bred for quality over quantity. Their body shape, color, and pattern are carefully developed over generations to meet strict standards. One of the most rewarding aspects of owning Japanese koi is watching their beauty evolve as they grow — their skin brightens, their shape improves, and their patterns become more defined. In contrast, domestic koi often reveal more imperfections over time and rarely develop the same elegant form.

While many koi sold as juveniles (Tosai) are 5–8 inches, with the right environment and nutrition, Japanese koi can reach over 30 inches in length — and in recent years, some have even exceeded 40 inches. Varieties like Chagoi, Karashigoi, and other muji iro (solid-colored) koi are especially known for fast and impressive growth. Quality filtration, ample space, and strong aeration all contribute to reaching this potential — but high-quality koi food plays a crucial role in supporting long-term development and body structure.

Koi are valued based on several factors, including body conformation, skin quality, color saturation, pattern, variety, and age. One of the biggest distinctions in pricing comes down to hobby-grade vs. show-grade koi. Show-grade koi meet strict standards for proportion, skin luster, and balanced patterns — and are often bred from elite Japanese bloodlines. Female koi typically carry higher price tags than males because they grow larger, develop wider and more balanced body shapes, and have more visual presence. Many of the most valuable koi are sold through breeder-hosted auctions in Japan, where a single fish can sell for thousands or even hundreds of thousands of dollars. Even Tosai (one-year-old) koi can carry a high price if they show potential to develop into show-quality adults. In contrast, hobby-grade koi may still be beautiful but lack the structure or pattern quality that holds up over time.

In the Japanese koi industry, koi are categorized by age using these terms:

- Tosai – 1-year-old koi, typically under 12"

- Nisai – 2 years old, often 12–20"

- Sansai – 3 years old, often 20–26"+

- Yonsai – 4 years old, often 26–30"+

Koi are judged and priced based on length and body shape, not weight. While age often correlates with size, it’s not always exact — some koi grow faster than others depending on genetics, food, water quality, and space.

Some collectors prefer to buy older koi (Sansai and Yonsai) because the body shape, skin quality, and pattern are more fully developed — essentially a more “finished” koi. Others enjoy purchasing high-end Tosai from elite breeders to watch their growth and transformation over time. Many enjoy a mix of both approaches.

A general rule is that many koi can reach their peak beauty by Sansai, but others continue to develop more pattern, depth, and refinement as they age — making their evolution part of the long-term enjoyment.

Color and pattern changes are a natural part of koi development — especially during the Tosai (1-year-old) stage. These changes can be unpredictable, but experienced hobbyists and breeders who understand bloodlines and koi development can often make educated predictions. Knowing the breeder and parent stock is key to anticipating how a koi might evolve.

Seasonal changes also play a role. For example, Goshiki often appear darker in colder water during winter and lighten in warmer months. Koi with sumi (black) patterning can be especially variable — varieties like Kumonryu and Matsukawabake are known for dramatic shifts in black markings, sometimes appearing to be completely different koi over time.

These changes are part of what makes koi keeping so exciting — watching a koi transform as it matures is one of the great joys of the hobby.

When evaluating a koi, focus on three main elements — in this order:

1. Body conformation – A strong, symmetrical frame with good volume, smooth taper, and balanced proportions. Body shape has the most visual impact and is the foundation of a beautiful koi.

2. Quality – This includes the skin’s luster, the depth and clarity of the color, and the scalation (the arrangement and cleanliness of the scales). These elements are often tied to genetics and bloodline.

3. Pattern – The placement, flow, and balance of markings across the body. While pattern contributes to beauty, it’s secondary to conformation and quality.

The body is the canvas — it carries the pattern. Even the most beautiful markings won’t have the same impact if the koi has a thin or unbalanced frame. The visual power of a koi comes from how these elements work together, but conformation always comes first.

True quality isn’t always obvious to beginners. That’s why working with a reputable dealer is so important — they can help identify koi with potential, especially at younger stages like Tosai. And as your experience grows, you’ll gain a deeper understanding of what makes a truly high-quality koi.

The best Japanese koi are selected in person from top breeders, packed in oxygenated bags, and flown directly to certified U.S. importers. Once they arrive, koi undergo a quarantine process that typically lasts several weeks to a month or more. During this time, the fish are monitored closely for health, slowly adjusted to local water parameters, and often tested or treated proactively to prevent the spread of parasites or disease.

Quarantine is a critical step in protecting both the imported koi and the buyer’s pond. It ensures that the fish are healthy, stress-free, and properly acclimated before being offered for sale. Working with a dealer who follows a responsible import and quarantine protocol is essential for long-term koi health and peace of mind.

Japanese koi are very peaceful and non-aggressive by nature. They can live with goldfish and some other cold-water, non-aggressive species. However, most koi hobbyists prefer to keep only koi in their ponds — both to fully appreciate their beauty and to avoid problems with feeding, compatibility, and water quality.

Aggressive or overly active tropical fish, like African cichlids, are not recommended. These fish often outcompete koi for food by swimming faster and eating more aggressively. This can result in koi becoming underfed or malnourished over time. In addition, koi require high-quality, specialized food — and feeding that to tropical fish not only wastes your investment, but may also harm the other fish if the diet isn’t appropriate for them.

While koi can coexist with other peaceful species in the right conditions, a koi-only pond is often the best way to maintain balance, highlight their beauty, and support long-term health.

Japanese koi are often called hardy, and they can survive in a wide range of conditions — but there’s a big difference between surviving and thriving. To reach their full potential in body shape, color, skin quality, and overall health, koi need excellent care.

That includes:

- Consistent, high-quality filtration

- Proper oxygenation and circulation

- Regular water changes

- A balanced, premium diet appropriate for the season

Without good care, koi may survive, but their growth will be stunted, colors can fade, skin quality may dull, and body shape may develop unevenly. These long-term effects can prevent them from reaching the level they were bred for — both in beauty and in health.



Proper care is essential if you want your koi to truly live up to their potential as living art.

Japanese koi come in many varieties, but the Gosanke — Kohaku, Showa, and Sanke — are considered the most prestigious and foundational.

- Kohaku – A white koi with red (hi) markings. It is said that “koi appreciation begins and ends with Kohaku,” making it the most iconic and respected variety.

- Showa – A black-bodied koi with red and white markings. Known for its bold contrast and powerful presence.

- Sanke (Taisho Sanke) – A white-bodied koi with red and black markings. Similar to Showa but with a lighter feel and no black on the head.

Other popular varieties include:

- Shusui – A scaleless (doitsu) koi with light blue skin and red markings along the lateral line.

- Yamabuki Ogon – A solid metallic yellow koi, bright and eye-catching in any pond.

- Goshiki – A multi-colored koi with red, white, and dark blue-gray reticulated scaling that often shifts seasonally.

- Chagoi – Solid-colored brown or olive koi, famous for their size, fast growth, and friendly behavior.

Some collectors enjoy building a pond with visual contrast among multiple varieties, while others prefer to focus on a single type and track its development over time.

Japanese koi are among the longest-living ornamental fish. With the right conditions, they can live 25 to 35 years or more. The most important factors influencing longevity are water quality and food quality. Clean, stable water and a high-quality, well-balanced diet are essential for supporting long-term health, immune strength, and steady development.

Other factors like genetics, pond size, and seasonal care also contribute, but without good water and nutrition, koi will rarely reach their full lifespan or potential.

In Japan, Tategoi refers to a koi selected by breeders for its future potential. These koi may be young (often Tosai) and not fully finished in pattern or color — but they show signs of excellent body conformation, high-quality skin, and strong lineage.

Breeders often hold back their Tategoi to grow another season, expecting them to develop into high-grade or even show-quality koi. Tategoi are not always the most eye-catching koi today — they’re chosen for what they will become over time.



Many serious hobbyists enjoy buying Tategoi for the challenge and excitement of watching them transform. That said, it takes experience to recognize true potential, so working with a knowledgeable and reputable dealer is important when buying Tategoi koi.