These fish are called "sharks" because of their sleek body design, but they are in reality true bony fish. They are cyprinids, distantly related to barbs, danios, minnows, and carp. I see these fish recently being sold at chain pet stores a lot, usually as small juveniles.
I want to be sure that people know these things grow quite huge--adults grow to a foot, believe it or not! As such, they need room to grow and should only be kept in tanks of 60 gallons and above to start (even then, you may need to upgrade later).
They are not a flashy color, but their silver color and hardy disposition are attractive. They are not picky and will eat all sorts of fish foods. The other nice thing about them is that they are one of the few larger fish that can usually be kept safely with smaller tetras, which they will be peaceful around.