[Scand.] The opening by which fishes breathe (q.v.), and the flap which covers it. Gills are usually thin fringes or plates, through which the blood circulates, and in which it is exposed to the action of the water, from which it absorbs oxygen. The gills of shrimps are the bag-like flaps that hang down where the legs join the body. The gills of an oyster are a delicate transparent frill of four-striped bands.