Ultimate goal is the reproduction of the fish to survive the species to which they belong. The fish are divided into oviparous, that is, the females lay eggs that typically are fertilized externally, and ovoviviparous, where fertilization occurs within the body of the female, where the embryos, independent of the maternal body are developed to be born, that is, out already as a small fish capable of independent life. Food for the small fry is in proportion to size, and require almost microscopic food, as food powder, or addition of water that contains tiny green algae.

oviparous fish
 The most common is to spread the eggs into the water. The mature female is stimulated by the male, often chased and knocked until it makes the eggs at this time the male emits sperm and eggs are fertilized in the water. The risks that the eggs are to be eaten by other fish to be exposed to sudden temperature changes etc.. I exhibit an example of the cichlid family of freshwater, they are loving parents and lay their eggs in cavities of rocks or in open spaces but well supervised. In some species of African cichlids for added security, the female broods the eggs in his mouth and still retains the fry after they hatch.

livebearers
These fish have a gestation period of about 30 days, the eggs fixed in the body of the mother and the embryos develop independently from this, taking food only from the egg substances. At the end of spring from 10 to 200 fry that swim freely once. In species where the female is small fry born one at a time, in days. In fact some of the family poeciliids females can give birth without having to mate with the male litters, because it can store the sperm inside the body.