Bony fish scales are made of bone and look like the shingles on a roof. Fins move, stabilize and sometimes protect the fish. Some fish do not have all of these fins, and their placement shows great variability. The very flexible fins of most bony fish have visible supporting rays and spines. The skeletal supports of cartilaginous fish fins are not visible, and these fins are fairly stiff.
Oxygen enters the bloodstream at the gills.
The gills are feathery structures found along the sides of the head. The gills of a healthy fish are bright red due to the large amount of blood present. In bony fish the gills are usually covered by a bony plate called an operculum. In sharks there are five to seven gill slits on the sides of the head which allow water to pass out of the gill cavity. The eyes of most fish are well developed.