Koi fish generally stop growing significantly when they are 2 to 3 years old. The growth rate of koi fish is relatively fast in the first six months, increasing by 0.71 millimeters per day. After that, the growth rate gradually slows down, increasing by 0.58 millimeters per day from 6 to 12 months, and by 0.54 millimeters per day in the second year. An ordinary koi fish can grow to more than 40 centimeters in length within 2 years. However, if there is insufficient space for breeding, it may only grow to about 30 centimeters.
The growth of koi fish is affected by various factors, including genetics, nutrition, and environmental conditions. Genetic factors have a significant impact on the growth of koi fish. Different varieties of koi fish may have different growth rates and final body sizes. In addition, the supply of nutrients and environmental conditions will also affect the growth rate and final body size of koi fish. If the breeding environment is small, the growth of koi fish may be restricted.
To promote the healthy growth of koi fish, it is recommended to provide sufficient breeding space and a good water quality environment to ensure that koi fish can stretch and move fully. In addition, reasonable feeding and nutritional supplements are also crucial to ensure that koi fish can obtain enough energy and nutrients to support their growth.