get food for them and those 4 fish will soon be 1 or 2 because the more dominant and bigger ones generally eat the weaker smaller ones unless their the same size but soon one will grow larger than the rest and you will end up with one fat fish and thats it. So i would get a larger tank in the near future just a heads up.
For food i would get, flies, worms, brine shrimp, smaller fish if possible, ants, termites, nats, mosquito larvae, get water samples fro mthe lake the fish were collected and that will contain copeods (think thats how you spell it) and thay are microspopic organisms the fish eat, and thats basically it until they get larger. You can also try flake food but generally bass like live prey, but its worth a try because live food gets expensive