Instructions
Look at the fins of the koi. Females have larger fins than males. Female fins also have less color and are rounder and more opaque on the edges. Male fins have more color and are pointier on the edges. However, while their fins are bland, females' bodies are very colorful.
Observe the size of the fish. Female koi are generally larger and rounder than males. This allows them to carry eggs for reproduction. A koi that is more than two years of age is more than likely much fatter because it is filled with eggs. Male koi fish are thinner, often looking like a long cigar.
Watch their activity. Female koi are often much slower and less active than males. If a koi is merely floating or moving apathetically, it is most likely a female. Males tend to move at a faster pace and show more curiosity.
Observe their eating patterns. If a koi is faster to reach the food but brings it to the mouth of another koi, it is a male. If the koi is sitting still while other koi bring it food, it is a female. This behavior occurs when a female is going to produce a spawn and cannot reach food quickly. The males bring it food until it produces its offspring.
How to Tell if Koi Are Male or Female
Koi fish are great additions to ponds because they have low maintenance requirements and they are aesthetically pleasing. They come in a variety of interesting colors and patterns, and watching them swim can be soothing and relaxing. Differentiating male Koi from females is difficult because the two share many characteristics. However, some subtle differences can help you determine the gender of a koi.