Pilotfish

pilotfish Naucrates ductor, a cosmopolitan fish of tropical and sub-tropical waters which wears six or seven broad black vertical bands on its silver sides and has a maximum length of 60 cm (24"). This fish takes its name from its habit of accompanying ships, and large sea creatures such as sea turtles and sharks, as though piloting them. Wheeler (1979) writes:

The association has not been explained satisfactorily; amongst the suggestions advanced are shelter in the shade of the larger object, increased possibilities for foraging on waste scraps from meals, and even the shark’s excrement. It is possible too that the pilot fish acts as a cleaner of parasites from its host. In any event the bond is evidently a strong one for Naucrates have accompanied turtles wandering as far as the inhospitably cold waters of England, far outside their normal range.