Fish can begin to reproduce after sexual maturity, but fish in the wild usually wait until the breeding period. Male and female fish entering the breeding period will be paired. After successful pairing, they will find a suitable place to lay eggs and fertilize. Some fish have the habit of protecting fertilized eggs, while others do not. Fertilized eggs hatch slowly until they become larvae. Usually, the smaller the fish, the stronger the reproduction ability, and the larger fish will have more difficulty in reproduction.

1. Oviparation: Oviparation is the reproductive method of most fish. Generally, females produce eggs, then males fertilize and hatch in water. This kind of fish is characterized by a large number of reproduction, because fish eggs are easy to eat, so it is necessary to multiply in large numbers to ensure the survival of offspring.

2. Oviparous: Oviparous fish are generally small fish of killifish family, such as guppy, Mary fish, moonlight fish, swordtail fish, etc. When they reproduce, male fish will inject sperm into female fish, and female fish will combine them with eggs at an appropriate time, and after a period of time, small fish will be produced.

3. Viviparous: Few fish are viviparous, and most viviparous fish are oviparous, that is, fish eggs hatch in fish, but there are viviparous species in sharks, and fertilized eggs absorb the nutrition secreted by the mother, instead of relying entirely on yolk sac for growth and development, so the reproduction mode is safer.