John Dory, also known as St Pierre or Peter's Fish, refers to fish of the genus Zeus, especially Zeus faber, of widespread distribution. It is an edible benthic coastal marine fish with a laterally compressed olive-yellow body which has a large dark spot, and long spines on the dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

. The dark spot is used to flash an 'evil eye' if danger approaches the John Dory. Its large eyes at the front of the head provide it with bifocal vision and depth perception, which are important for predators.