The ocean is full of hungry predators, and the fishes in the four families shown here have all developed a defensive weapon on their bodies. Triggerfishes and filefishes both have a very sharp first dorsal spine. Boxfishes have platelike scales that form a stiff, protective armor -- like a box -- around their entire bodies. Surgeonfishes have two scalpel-like spines on their underside (at the base of the tail fin) that can be extended as a kind of spike. Like the other surgeonfishes, the pretty Blue Tang is among the most noticeable fishes on coral reefs. It is usually bright yellow when young and generally becomes bright blue as an adult.

Look For: A compressed, deep-bodied, almost disk-shaped blue surgeonfish with yellow spines on the base of the tail fin.

Length: 14".

Habitat: Coral reefs.

Range: Atlantic coast (strays north as far as New York) and Caribbean; may also live in Gulf of Mexico.