The blue shark, Prionace glauca, with an accompanying Pilot Fish, Naucrates ductor, in clear blue tropical waters. Sunlight dapples the upper surface of the shark.The blue shark is an oceanic shark found worldwide in deep temperate and tropical waters from the surface to about 350 meters. Although generally slow moving, it is capable of moving very quickly. It feeds primarily on small fish and squid, and sometimes bigger prey. The pilot fish (Naucrates ductor) is a widely distributed carnivorou