In some species, parents abandon the eggs, which develop without help; sometimes the mother has prepared a nest for them; sometimes she watches over them after fertilization; but very often the father takes charge of them: as soon as he has fertilized them, he chases away the female, who tries to devour them; he fiercely defends them from anything that approaches; there are those that put up a kind of protective nest by emitting air bubbles covered with an isolating substance; they also often incubate the eggs in their mouths or, like the sea horse, in the folds of the stomach.