How Big Can Koi Grow? A Detailed Explanation of Adult Koi Body Length

Koi can grow to 1-1.5 m. If kept in a small fish tank, due to the limited space for activity, they can only grow to two or three cun; if you want them to grow big, they should be kept in a large fish tank or an outdoor pond, and they will quickly grow to 30 cm or larger.

How Do You Tell Male and Female Koi Apart?

1. Look at body shape: those with a plump belly are female; those with a slender body are male.

2. Look at the vent: a wide, flat vent indicates female; a small, sunken vent indicates male.

3. Look for breeding tubercles: when males are about to release sperm, small breeding tubercles, known as breeding stars, grow on the head and pectoral fins. During the breeding season, those without breeding stars are female; those with breeding stars are male. Gently pressing the belly of a mature male will release white milt.

4. Feel the fin rays: those with rough, keratinous protrusions are male; those that are smooth are female.