Tosai, Nisai or Sansai: What Age of Koi Should You Buy?

Japanese koi are sold by age before they are sold by anything else. Tosai is a koi in its first year, nisai its second, sansai its third, yonsai its fourth. The words matter because the same bloodline, bought at a different age, is a different purchase: a different price, a different amount of risk, and a different amount of the fish's story that you get to own.

We buy at every age, and on the 2026 winter trip Zak bought tosai by the hundred, two-year-old Kohaku by the handful, and one seven-year-old Kujaku for a client. This is what each age actually gets you, using those fish as the examples.

Tosai: you are buying a guess

A tosai has done almost none of its developing. The body is roughly set, the skin is beginning to show what it will be, and the pattern is still moving. Zak's honest reason for loving them, said at the Oya auction: "I love babies. Tosai, 'cause you never know what's going to happen."

The breeders say the same thing from the other side. At Tani, asked what is most fun about Beni Kumonryu, the answer was that they change and you don't know what will happen. Asked what they will look like at five, "you don't know. You really don't know." At Oyama, the darkest, least attractive young Mukashi Ogon were the ones with the best chance of growing big. At Omosako, the Kujaku to buy small were the dark ones, not the pretty ones. The whole skill of buying tosai is reading a fish for what it will become, and we wrote that up on its own in buying tosai.

Two things people get wrong about tosai. First, that bigger is better. Zak buys them small on purpose: "I like them smaller. The quality is the same, I just like them smaller because you can ship more in a box and they have a higher chance of being happy and healthy when they arrive." Second, that a tosai is a small fish. At Kanno we saw tosai from a Momotaro bloodline cross at 45cm, which Zak called "huge for a baby"; Kazuhiro Hirasawa's view was that "they definitely will get a meter long." Age is age. Size depends on the bloodline and the pond.

Tosai is also the age at which the breeder keeps the best for himself. Every farm sorts a year's fish into tategoi, the ones it keeps to grow on, show or breed from, and tateshita, the rest. The tateshita are what is for sale. At a farm like Ogata, tateshita is still a very high bar, and the tategoi are not for sale at any ordinary price: "you have to really fight for it in order to get it."

Nisai: the sweet spot

A two-year-old has been through a second summer, usually a mud pond, and has started to declare itself. Body shape is clearer, skin quality is readable, pattern has settled enough to judge without being finished. It is also the age Zak keeps wishing he had bought more of.

At Marusei he bought twenty to thirty two-year-olds, mostly Gosanke, and the way he chose the Kohaku says what nisai are for: "We're making sure we get the ones that have the most unique and clean patterns. They're all two years old." You can choose a two-year-old for a clean pattern because the pattern is mostly there. You cannot do that with a tosai.

At Kaneko, nisai is the age Zak buys Shiro Utsuri, every year. At Ogata, he watched the staff filming two-year-olds for the February auction and said, looking at one in the bowl, "actually, maybe I should have bought more of those kinds."

There is one kind of two-year-old that looks like a tosai and isn't. At Otsuka, Zak pointed out a tank of small fish: "You can call them bonsai koi, or shimeni. They're actually all two years old, even though they look like they're one. You keep them small because it makes the colours develop really nicely, and they're very healthy. Just because they're not enormous doesn't mean they're not healthy." If you want finished colour in a small pond, that is the fish to ask about.

Sansai and older: a finished koi, or close to it

From the third year on, you are increasingly buying the fish in front of you rather than the fish it might become. Yusuke Ogata put the two cases side by side in What Makes Koi Beautiful. One Showa, four years old, was what breeders call a finished koi: "It's black everywhere. Nothing is coming." A Ginrin Showa of three was "not finished yet," and he valued it for the sumi still to come. Both were about 70cm. The difference between them was not size or age so much as how much of the story was still unwritten.

Older fish are also where the breeders' patience pays off, which is why many of them never leave the farm. Mr. Taniguchi kept a white koi with a great body for three years before its pattern arrived; it is 95cm now and has won awards. At Ogata there is a whole greenhouse of azukari fish, bought by customers as tosai or nisai and grown out at the farm year after year. The three tategoi Zak agreed at Taniguchi this trip are staying in Hiroshima for a year for the same reason: Mr. Taniguchi will grow them better than anyone can in a box on a plane.

And sometimes an older fish is simply the right fish. At Omosako, Zak bought an 82cm, seven-year-old female Kujaku for a client who, in his words, "doesn't really care that much about shows. He just loves koi for the love of koi." She has a window on one side and some scales not quite dark enough for a judge, and "her body is absolutely stunning, and the beni is so deep." Nobody is waiting for her to become anything. She is done, and she is beautiful.

So which should you buy?

• Buy tosai if you want to learn, if you want several fish for the price of one older one, or if you want the years of change for yourself. Buy a few, not one, and accept that some will not turn out.
• Buy nisai if you want a fish you can judge properly today and still watch develop. It is the age where a clean pattern, a good body and a fair price overlap most often.
• Buy sansai or older if you want the finished fish, for a show or for the pond, and you would rather pay for certainty than wait for it.

Whatever the age, the rule Zak repeated at every farm applies: "You're not buying the koi you're looking at, you're buying the future koi." With a tosai, that is the whole purchase. With a seven-year-old, it is a reminder that even a finished fish, as Yusuke said of his champion, "goes up and down every year."

Browse our tosai, or every koi we currently have available, each listed with its year born. For how the fish are chosen at the farms, read how buying koi in Japan actually works. Live koi ship Tuesdays and Wednesdays, anywhere in the USA.