The sumi in koi typically begins to stabilize around four to five years of age, though this can vary depending on lineage and individual traits.
What patterns or trends are observed in the changes of sumi in koi?
The development of sumi is influenced by variety, bloodline, and environmental temperature, and often varies with seasonal shifts. Generally, sumi appears most vivid at temperatures around 15–16°C, while it may recede or fade at temperatures above 25–26°C.
Koi varieties with prominent sumi patterns, such as Taisho Sanke (White-based Sanke) and Shiro Utsuri (White-ground Utsuri), can look dramatically different as adults compared to when they were young—sometimes to the point of being unrecognizable as the same fish. Varieties like Kumonryu may show completely different sumi expression in high versus low temperatures, and Goshiki also exhibits notable changes in its sumi under varying temperature conditions.
The variability and unpredictability of sumi development is considered one of the most fascinating aspects of keeping and appreciating koi.
