Species with internal fertilization tend to have females care for the young because the male is the one who can leave first. He can maximize his reproductive success by searching for other females while the female is left with the choice between putting a lot more time and energy into caring for the offspring or leaving them to die.

Species with external fertilization have the opposite dynamic. The female lays unfertilized eggs and then leaves. The male is the one stuck caring for them because they would die otherwise. However, the males of some species have evolved to be too clever for this:

Among the maternal mouthbrooding cichlids, it is quite common … for the male to fertilise the eggs only once they are in the female’s mouth.