There are two different techniques of breeding, with which we separate fishes in two great groups, the livebearers and the egg layers .
Live bearing is a more primitive behavior than egg laying.
The livebearers give birth to formed fishes as fertilization takes place inside the bodies of the parents as their ancestors did. This is the easy part. But let us take a look at the breeding events taking place among what we call egg layers. Many species are free spawners . These species breed either in pairs or in schools.