Naucrates Ductor

– Pilot Fish –

The pilot fish (Naucrates ductor) is a carnivorous fish of the trevally, or jackfish family, Carangidae.^[3] It is widely distributed and lives in warm or tropical open seas.

Description

The pilot fish congregates around sharks, rays, and sea turtles, where it eats ectoparasites on, and leftovers around the host species;^[4] younger pilot fish are usually associated with jellyfish and drifting seaweeds.^[5] They are also known to follow ships, sometimes for long distances; one was found in County Cork, Ireland,^[6] and many pilot fish have been sighted on the shores of England.^[7][8] Their fondness for ships led the ancients to believe that they would navigate a ship to its desired course.^[9]

The pilot fish’s color is between dark blue and blackish-silver, with the belly being lighter in color.^[10][11][12] The pilot fish is also known to have a temporary variation of color when excited; its dark-colored bars disappear, and its body turns silvery-white, with three broad blue patches on its back.^[13] It can be recognized by its five to seven distinctive traverse bands,^[14] which are of a much darker color than the rest of the body.^[11] The pilot fish can grow up to 60–70 cm in length.^[15]

This fish belongs to the trevally family. It measures approximately 35 cm. Males can reach 41 cm and females 43 cm (observed record of 63 cm). His body is fusiform , slender and barely compressed. Five to six broad dark bands (black, bluish) vertically zebra its silvery body covered with very small and rough scales (ctenoid *).
The commissure of the jaws ends below the level of the anterior edge of the eye. The very small teeth are arranged in a band on the two jaws.
The base of the anal fin is shorter than that of the dorsal fin. The pectoral fins are equal to or slightly shorter than the pelvic fins. The forked and bilobed tail is terminated in white spots .
Unlike other species of its family, the pilot fish does not have scutes on the caudal peduncle but a fleshy lateral keel.
The lateral line is slightly to moderately arched above the fins.

The pilot fish is edible^[16][17] and is said to taste good,^[18][19] but it is rarely available due to its erratic behavior when caught.^[20]

While pilot fish can be seen with all manner of sharks, they prefer accompanying the oceanic whitetip, Carcharhinus longimanus.^[21] The pilot fish’s relationship with sharks is a mutualist one; the pilot fish gains protection from predators, while the shark gains freedom from parasites.^[22] It was often said by sailors that sharks and pilot fish share something like a “close companionship”;^[23] there were even tales of this fish following ships which had captured “their” shark for up to six weeks^[24] and showing signs of distress in its absence.^[25][26]

Whatever the veracity of such reports, it is extremely rare that a shark will feed on a pilot fish,^[27] and smaller pilot fish are frequently observed swimming into sharks’ mouths to clean away fragments of food from between their teeth. As Herman Melville put it,^[28]

They have nothing of harm to dread,

But liquidly glide on his ghastly flank
Or before his Gorgonian head;
Or lurk in the port of serrated teeth
In white triple tiers of glittering gates,
And there find a haven when peril ‘s abroad,

An asylum in jaws of the Fates!^[29]

These observations have led to the pilot fish’s distinctive markings being copied for decals supplied as shark protection for surfboards.^[30]

Etymology and Metaphors

There are a few possible, conflicting etymologies for the term “pilot fish”. One is that seafaring people believed that pilot fish, which would appear around the bow of their ships when they were close to land, were leading (or piloting) them back to port.^[31] An alternative etymology is that pilot fish were once, erroneously,^[32] thought to be piloting sharks to food,^[33][34] or even (as legends have it) piloting ships, whales and swimmers to safety.^[35]

In Greek mythology a sailor called Pompilos helped the nymph Okyrhoe when she was fleeing away from the god Apollo. The sailor moved the nymph from Miletus to Samos and the god punished him by making him a pilot fish.^[36]

The pilot fish is sometimes used as a metaphor or simile; “they are like the pilot fish to the shark, serving to lead him to his victim”.^[37] Pilot fish are also used as a metaphor or simile for scavengers or looters which accompany a greater threat.

Biotope

Naucrates ductor is epipelagic oceanic . It is a symbiotic commensal or mutualist fish with large pelagics (sharks, rays, turtles, whales). Juveniles are associated with rafts of algae, floating debris, fish aggregating devices (FADs) or large jellyfish, nits and therefore easier to follow.

Similar Species

With its vertical black bands and its behavior as a follower of large pelagics, it is difficult to confuse the pilot fish. It is easily distinguished from another follower fish, the remora ( Echeneis spp), because it does not cling to its partner like the latter, but follows it actively swimming.
It is the only representative of the genus Naucrates . There is probably no speciation of the genus as fish can travel long distances with their host in almost all warm and temperate seas allowing for significant genetic mixing.

Alimentation

The pilot fish takes advantage of the remains of meals from its travel partners, and feeds on the ectoparasites of the latter. Associated with a DCP, it is planktonivorous and feeds on larvae of gastropods, amphipods, crustaceans and fish (ex: Atlantidae, decapods, Hyperiid amphipods, Alciopides polychaetes)
The stomach contents of 80 individuals (between 21 and 29 cm , standard length)captured in the central Mediterranean were analyzed between October 1994 and January 1995. It was observed that the predilection prey were pelagic crustaceans (in particular Hyperiid amphipods). Pelagic gastropods (Atlantidae) and fish larvae followed, in smaller quantities. The study tends to show that the pilot fish have a planktonophagous diet up to a size of about 30 cm, or 6 months of age. However, the largest individuals escaped this study because having abandoned FADs and other floating objects in favor of the pelagic environment, they could not be fished.

Reproduction

The 2 to 3.9 mm * pelagic * larva grows rapidly. This fish can reach 30 cm during the first six months of its life spent in groups near floating objects. At this size, he is then sexually mature. In summer, it will lay oval eggs with a large perivitelline space, after external fertilization.

Associated Life

The association with large pelagics is characteristic of this fish. This fish was called “pilot” because it was believed for a long time that the fish guided the sharks they accompanied. In fact, pilot fish are associated with sharks, whales or turtles, the favorite host being the oceanic shark ( Carcharhinus longimanus ). When fish lose their large pelagic (death, predation, fishing), they can be observed following boats or aggregated under FADs while waiting to find a host.

The pilot fish benefit from the hydrodynamics, food and protection of its host. The advantages of this apparently commensal host / pilot fish association are mutualistic when the latter rids its host of parasites.

Various Biology

Studies on this species are quite rare due to its pelagic nature, in adulthood.
The oldest captive fish lived for three years.

Further Information

The pilot fish is not shy, because it feels protected by its host. It is therefore easy to observe it as long as you are not too captivated by its host.

Pilot fish are difficult to fish except in certain Mediterranean areas where they are caught around FADs. They can be incidentally captured at the same time as their host.

In popular culture

In the BBC science fiction series Doctor Who, the pilot fish were used in analogical terms for a robotic species who congregated around more dangerous life-forms, such as the Sycorax and the Racnoss. They appeared three times in the series; twice with David Tennant in “The Christmas Invasion” (2005) and “The Runaway Bride” (2006), and once with Matt Smith in “The Pandorica Opens” (2010).

In the Discworld novel Making Money, during a conspiracy to entrap Moist von Lipwig, Heretofore reflects on his current predicament and uncomfortable relationship with Cosmo Lavish and says “Does he think he’s Vetinari? What do they call those fishes that swim alongside sharks, making themselves useful so they don’t get eaten? That’s me, that’s what I’m doing, just hanging on, because it’s much safer than letting go.”^[38]

Ernest Hemingway bitterly immortalised John Dos Passos as a “pilot fish” for the wealthy in A Moveable Feast, after falling out with him over the Spanish Civil War.^[39]