Most fish breed by spawning, or laying eggs, according to Petalia. Some fish species give birth to live babies. Spawning fish reproduce when males fertilize the eggs after they are laid, while livebearing females are directly fertilized by the males.

Baby fish often need assistance avoiding predators until they grow large enough to avoid being eaten. Once baby fish are born, the fishkeeper needs to provide cover so the babies are not eaten by their tankmates or their parents. This can be dense plant cover in the parents' tank, or the baby fish can be removed altogether and kept in their own fry tank.