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"How Old Is This Koi?"
By Joel Burkard/Pan Intercorp

Why is there never a simple answer to a question about koi? Japanese breeders use the name "tosai" to indicate koi that are less than a year old. The term has been adopted by koi keepers the world over, and is often confused or misused.

Most koi are spawned in May or June, and technically, the name "tosai" should only be used from the time they are harvested until the end of December. This means that "tosai" are available for purchase in the fall.

Once January rolls around, they become "ake nisai" or "early two year olds", and are no longer considered "tosai".

When they are again harvested in the fall, having lived through two growing seasons, they are referred to as "nisai" or "two year olds".

The Shiro Utsuri featured here was one of a number of tosai purchased by Mr. Seigyu Sawai via "mail order" from Koshiro Fish Farms in Niigata in the fall of 1991.


Shiro Utsuri

Shiro Utsuri
4 inches
January 1992


Shiro Utsuri

Shiro Utsuri
12 months old, 6.5 inches


Shiro Utsuri

Shiro Utsuri
15 months old, 12 inches


Shiro Utsuri

Shiro Utsuri
3 years old, 17 inches


The first photo was taken in January of 1992, and shows the ake nisai at a diminutive 4 inches. Although there is some evidence of the checkerboard utsuri pattern, it might be difficult to convince the average koi keeper that this koi was bound for glory.

In the second photo, the koi is a full 12 months old, and still only 6.5 inches long. Its pattern has begun to emerge and the white is definitely improving. The yellowish color on the head is typical of young Shiro Utsuri.

The third photo shows the Shiro Utsuri at fifteen months old, measuring just under 12 inches, a growth spurt of almost 6 inches in three months. We see that the black has emerged at the base of both pectoral fins in a classic example of "moto guro", and although the head is still a little yellow, the white is clearing rapidly.

Some breeders say that the yellowness on Shiro Utsuri can be improved by feeding food laced with terramycin. Others prefer to wait for the white to improve with maturity.

The fourth and last photo shows Mr. Sawai's Shiro Utsuri as a 17 inch three year old, Champion 45bu Utsurimono, at the 22nd All Kanto Show. Going back to the first photo, it's hard to believe that we are still looking at the same koi. The development of this koi is a truly amazing testimony to the process that is tategoi.