There are said to be more than 200 different varieties, probably over 500 if you take into account variants like Doitsu and Kinginrin. But for the sake of koi shows those varieties have been grouped into Show Classes where their unique characteristics can be judged in a like-for-like manner.
Koi shows first began as part of an agricultural fair in the village of Yamakoshi in the Niigata prefecture. Originally they were just exhibitions by the koi breeders of the area, but as their popularity grew they became competitions judged by consensus. After the Great Tokyo Exhibition in 1914 the Niigata farmers formed co-operatives and from these sprang the first Nishikigoi-only shows, which continued on a yearly basis until the outbreak of WW2.
The first Nishikigoi show after the war was held in 1951 just outside Nagaoka City. By 1960 there were several shows within that region. However, by then, they were not just breeder shows. Wealthy hobbyists had begun buying koi and keeping them in other parts of the country.
The breeders then turned over the judging of their shows to these hobbyists to ensure unbiased results. The rules of appreciation were entrusted to these hobbyists who eventually evolved into the ZNA (Zen Nippon Airinkai). ZNA documented them, and created the earliest show rules. It is from those that the formats of all shows in and out of Japan have evolved.
One of the early decisions was to set up Show Classes where varieties with shared characteristics compete against each other on a level playing field. Originally there were just 8 Show Classes (see right) but over time additional classes have been added (Hikari x 3, Tancho & Kinginrin) to accommodate their distinct characteristics. For many years these 13 Show Classes formed the bedrock of all Koi shows worldwide. Indeed the BKKS adopted them in 1989 when they formulated their first Show Rules & Guidelines.
ZNA allowed its member chapters to adapt the Classes to fit local preferences and nowadays it is not unusual to find up to 17 Classes in use in some shows.
However, here in the UK, the BKKS stick to the original 13 and details of each can be found in the series of short, Fact Sheets that are linked below.
Each will have a downloadable attachment.