Sardines have a flat body which is covered with large, reflective, silvery scales. In the middle of their belly, they have a set of specialized scales, known as scutes, which are jagged and point backwards. Having very small teeth or no teeth at all, sardines eat plankton, which they filter from the water through their gills . Sardines are small, silvery, elongated fishes with a single short dorsal fin, no lateral line, and no scales on the head. They range in length from about 15 to 30 cm (6 to 12 inches) .