Caring for newborn fish, also known as fry, is tricky. If the fish are a species that eats its young, remove the fry from the tank immediately to protect them from the adults. If the species cares for its young, keep them together with the mother in the tank.
Feeding fry is a challenge, since not all newborn fish begin to eat at the same time. Typically, live-born fish are larger and begin to eat almost immediately, while fry hatched from eggs subsist for about 48 hours by eating the yolk-sac in which they are born. Once large enough, however, both types of fry need a diet that is small enough for their tiny mouths and sufficiently nutritious to sustain them as they grow. Infusoria, microscopic organisms commonly found in fresh water, can be cultured in advance and fed to the fry several times a day. Freshly hatched brine shrimp, green water and commercially prepared fry-food are also good choices. Once the fish are about 1 or 2 weeks old, it is best to feed them ground-up flake, dried or pellet food several times a day.