Shark is the firm, meaty flesh of any of several hundred species of cartilaginous predatory fish (the superorder Selachimorpha), sold for the table mostly as the dense, boneless loins and steaks of smaller species such as spiny dogfish, mako and blacktip. Lean, pale and almost steak-like when fresh, it carries two persistent caveats: a high mercury load from its place near the top of the food chain, and a tendency to turn sharply ammoniated if the urea-rich flesh is not bled and chilled quickly after the catch.