Domestic koi fish reproduce naturally. As long as the fish is mature, and there are females and males, and the environment is suitable, koi will reproduce by itself. Before breeding, the fish will pair first, and the male fish will chase the female fish. After successful pairing, they can wait for the fish to breed. After breeding, the parent fish should be fished out in time to avoid eating the eggs. The fished parent fish should rest for a few days before being put back into the vat, and the fish eggs should be kept at a certain temperature, waiting to hatch.

1. Immature: The reason why domestic koi does not reproduce is probably because the fish is not mature yet. This kind of fish can only mature sexually in about 3 years, before which it can't reproduce. After sexual maturity, koi will estrus and mate. Therefore, if you want to breed, you must choose mature parent fish and put them together.

2. Sexual consistency: Koi needs at least one male and one female to reproduce. If all the fish are male or female, they can't reproduce naturally. Usually artificially propagated, in order to improve the probability of successful pairing, male and female fish need to be released according to a certain proportion. Generally, female fish should be 1: 3 than male fish, so that enough male fish can courtship.

3. Environmental discomfort: If koi fish feels environmental discomfort, such as too narrow space, insufficient oxygen, or low temperature, it will also cause it to be unable to reproduce. At this time, it is necessary to raise the water temperature and keep oxygenation. If conditions permit, it can be put into a special breeding tank.