1911 Encyclopædia Britannica/Pilot-fish
PILOT-FISH (Naucrates ductor), a pelagic fish of the family of horse-mackerels or Carangidae, well known to sailors from its peculiar habit of keeping company with ships and large fishes, especially sharks. It occurs in all tropical and sub-tropical seas, and is common in the Mediterranean, but becomes scarcer in higher latitudes. In summer pilots will accompany ships as far north as the south coast of England into port.
Pilot-fish.
This habit was known to the ancients, who describe the Pompilus as a fish which points out the way to dubious or embarrassed sailors, and by its sudden disappearance indicates to them the vicinity of land; the ancient seamen of the Mediterranean regarded it, therefore, as a sacred fish. That the pilot accompanies sharks is an observation which first appears in works of travel of the 17th century, the writers asserting that it is of great use to its big companion in conducting it and showing it the way to its food. It is, however, extremely doubtful whether the pilot’s connexion with a shark serves a more special purpose than its temporary attachment to a ship. It accompanies both on account of the supply of food which it derives from them. The pilot, therefore, stands to both in the relation of a so-called “commensal,” like the Echeneis or sucking-fish. All observers, however, agree that neither the pilot nor the sucker is ever attacked by the shark. The pilot attains to a length of about 12 in. In the shape of its body it resembles a mackerel, but is rather shorter, especially in the head, and covered with small scales. A sharp keel runs along the middle of each side of the tail. The first dorsal in consists of a few short spines not connected by a membrane; the second dorsal and the anal are composed of numerous rays. The teeth, which occupy the jaws, vomer and palatine bones, are all small, in villiform bands. The coloration of the pilot renders it conspicuous at a distance; on a bluish ground-colour from five to seven dark-blue or violet cross-bands traverse the body from the back to the belly. The pilot-fish spawns in the open sea, and its fry is constantly caught in the tow-net. But young pilot-fish differ considerably from the adult, having the spines of the first dorsal connected by a membrane, and some bones of the head armed with projecting spines. These little fishes were therefore long considered to be a distinct genus, Nauclerus.