pilotfish

[pahy-luh t-fish]

a small, marine fish, Naucrates ductor, often swimming with sharks.

any of various other fishes having similar habits.

Origin of pilotfish

First recorded in 1625–35; pilot + fish

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

He was made to stick to the skipper as though he were of some use—as the pilot-fish, they say, is to the whale.
End of the Tether
Joseph Conrad
One paper likened him to the pilot-fish, which guides the shark to his prey.
Andersonville, Volume 2
John McElroy
I must not forget to tell you something about the pilot-fish.
A Popular Account of the Manners and Customs of India
Charles Acland
There are other curious things about these pilot-fish that naturalists cannot explain.
Harper's Round Table, October 29, 1895
Various
The Pilot-Fish had long since departed for other scenes, and Sammy wished that he had consented to accompany him.
How Sammy Went to Coral-Land
Emily Paret Atwater

Word Origin and History for pilot-fish

1630s, from pilot (n.) + fish (n.). So called because they were thought to lead sharks to prey.