Growing KOI at Ebro Fish Farm Do you want to pick your own Koi in Japan and to be sure they grow and are healthy, we think we are the partner for you. Due to the perfect climate is the growing season for koi about 10 months guaranteed. From baby to Tosai the average growth is 20 to 30 cm in 1 season.   Your koi stay in separate tanks and are several times a day by hand. The food they get is a well-balanced diet. Water changing on a regularly base keeps the water quality very good. The koi are regularly monitored and measured.          Develepemont of a Sanke within one growing season.