How does a mammal provide parental care?

Well, firstly, all mammals care for their young, while only a few fish do.

Parental care in fish is also more variable in form than in mammals.

All mammals need to nurse from their mothers to survive, so obviously the mother is always involved. In most mammals, mom is the only one to care for her young, while a few mammal mothers get help from fathers, other mothers or their older offspring. However, the mother is always the most important.

In contrast, parental fish have pretty much every system imaginable. 80% of parental fish species only tend the eggs, and leave when the babies are born. Egg-tending can be done by mothers, fathers, or both, but most often it's done by fathers. (Indeed, seahorse fathers even carry their eggs in a pouch like a marsupial!) The 20% who care for their fry (baby fish) also vary a lot. Actually feeding their fry is rare, although some fish produce infertile eggs for fry to eat, and discus even produce a mucus on their skin that basically serves the same purpose as mammal milk. More often, parental care of fry involves protecting the fry from predators, either by attacking predators (usually a two-parent job) or carrying babies with them (as with mouthbrooding cichlids mothers, who hold babies in their mouth). A few species also have older fry stay and help raise younger siblings, but this is rare.