pilot fish

noun, plural (especially collectively) pi·lot·fish, (especially referring to two or more kinds or species) pi·lot·fish·es.

1. a small, marine fish, Naucrates ductor, often swimming with sharks.
2. any of various other fishes having similar habits.

noun

1. a small carangid fish, Naucrates ductor, of tropical and subtropical seas, marked with dark vertical bands: often accompanies sharks and other large fishes
2. any of various similar or related fishes