A sawfish rostrum is a flattened extension of the skull, lined on each side with a row of hard, pointed structures set in sockets. They develop as enlarged dermal denticles, the same skin scales that cover the rest of the body, rather than as oral teeth. A lost rostral tooth does not regenerate.
The saw does two jobs. Its surface is dense with ampullae of Lorenzini, electroreceptors that detect the faint fields of buried or hidden prey, so it works as an antenna held out in front of the animal. Experimental work with captive sawfish also recorded lateral swipes used to stun and impale fish in midwater.
The same organ makes the fish catastrophically easy to catch: the rostrum tangles in any net it touches. The smalltooth sawfish became the first marine fish listed as endangered under the United States Endangered Species Act, in 2003.