Tosai is the Japanese term for koi born last year.
These koi will have been spawned in May/June in Japan, and released in to the mudponds to grow to just a few inches before being heavily culled to save only the best fish. In September they are harvested, and placed in indoor ponds until the following spring. They are continually graded, with the very best kept in heated, heavily fed ponds to produce jumbo tosai (25cm+).
Spring time is generally when we will receive the larger shipments of tosai, though our use of a reputable UK wholesaler means we have access to thousands of tosai at any one time. It is always worth asking to source fish if we do not have them in stock.