Much used words in the koi industry.
Ages of koi;
Tosai; one year old koi
Nissai; Two year old koi
Sansai; Three year old koi
After a koi is born and had 1 summer season of grown it is then sold as tosai or kept by the breeder to grow a second season and is then sold as a two year old koi named a nissai. A koi that has been with the breeder for three years is called a Sansai.
It will be obvious that the breeders keep the best tosai to sell for a higher price after a second growing season.
Mud ponds, these are the koi ponds in which they are grown in the summer.
Tategoi, koi that can improve (very roughly translated). also: The most expensive koi in the hobby, but not the expensive fish in the average koidealer ponds.. Trust me, real tategoi are not easily sold by the breeders in Japan because these are the ones to make money with in the future. (unless the asking price is paid but these are extremely high for very small koi, far above the 1000 to tens of thousends of euros for 40cm ..)