How do determine the sex of koi?
Male koi are mostly thinner and usually have larger pectoral fins, the anal opening is a slit form. In our climate sexual maturity is reached after 3 – 4 years.
Female koi are rounder, have smaller pectoral fins and a round anal opening. Sexual maturity is reached at app. 4 – 5 years. Precise identification is not possible for young fish.