Many fish lay eggs, but some -- including common aquarium fish such as guppies, swordtails, and mollies -- retain the eggs inside their bodies until hatching. In a few, such as the seahorse, the male receives the eggs and keeps them inside a special pouch in his body. Such fish are said to be ovoviviparous; unlike mammals, these fish do not nourish the embryos during development. Many fish do not provide any care for their offspring, but a number do protect them in various ways. In some African cichlids, for instance, the female keeps her eggs in her mouth -- and after they hatch, the young are kept in her mouth as well.