my small dats feed on freezed dried shrimps, bt the big ones take fresh market shrimps, both get some bloodworms every two days. And if ur lucky, they mite also take pellets, floating and sinking.
When picking fish, just make sure they have good fins, clear eyes, no red around the gills and no obvious scale problems. In fish shops they are usually hiding, u can see if they ar active by dangling your hands over the tank, they usually dart out.
Dont worry if the colour of the dat, it may seem washed out and spickly. But this'll probably go away once you take it home. From then on, the stripes can come and go depending on tempreture, diet, tankmates, its territory, water parameter. And if kept in groups, try to keep them in groups of 3 or more.
They are fantastic fish and develope fantastic personalities, mine rockets outta nowhere when it sees me, bt completely ignores my gf. Hehehe, enjoy the fish!