Fish have babies by either laying eggs or bearing live young. In live birth, the eggs are carried inside the mother until they hatch. She will then give birth to the fry or pups.
In some fish, such as sharks, the embryos are nourished by a placenta-like organ until they're developed, at which time the mother births live young. Some fish, such as codfish, which release eggs and sperm into the water, don't offer their young or eggs any parental care. Others, like Siamese fighting fish, build nests to protect the eggs. Some sharks that hatch inside their mother eat their siblings and other eggs before they're born.