Bony fishes

Jacks, Amberjacks, PompanosCarangidae

Family30 species

Almost every large fish on a reef has an address. A jack does not. This family belongs to the open water off the edge, and it comes in over the coral the way weather does: a bar of silver at the limit of visibility that is suddenly overhead, moving, and then gone toward the drop-off. Nothing else that size on the reef is so obviously a visitor.

The family gave its name to the way it swims. In carangiform swimming the front two thirds of the fish stays rigid and only the rear section and the tail move, which costs far less than the whole-body wriggle a reef fish uses and holds a line at speed. The tail stalk is narrow and stiffened along each side by a row of bony scutes, and the tail itself is a deep, stiff crescent, a propeller rather than a paddle. Tuna arrived at the same answer in a different family.

The hunting is timed. Trevally work the reef edge hardest in the twenty minutes around dusk, and again at first light, when the day fish are dropping into the coral, the animals that feed at night are not out yet, and the light has gone too poor for a small fish to see a large one coming while it is still good enough for the large one to see it. Groups split a school of fusiliers against the surface or against the reef wall, where a fish that turns has nowhere to turn to.

Thirty species are listed here, from scads the length of a hand to the giant trevally at 1.7 m (5.5 ft). If the reef in front of you goes quiet and the small fish compress into a ball against the coral, look out into the blue rather than at the reef.

How to recognise jacks, amberjacks, pompanos

TorpedoStreamlined and muscular, built for open-water speed - jacks, tunas, barracudas.

streamlined, often compressed body
deeply forked tail fin
two dorsal fins, the first with short spines
lateral line often armed with bony scutes near the tail
generally silvery, grey, or brassy coloration

30 species in Jacks, Amberjacks, Pompanos

Alectis

Deep, flat and silver, like a plate held on edge, with a forehead that drops almost vertically. The young trail thread-like filaments several times their own body length; the adults lose them completely and look like an entirely different fish.

Alepes

Scads: small schooling jacks of shallow inshore water, and the only ones on this page that live on plankton rather than on fish. The diet is shrimps, copepods and decapod larvae, which is where the English name of the commoner one comes from. One of the two has been through the Suez Canal and now lives in the Mediterranean as far west as Malta.

Carangoides

Separated from Caranx by the head. The mouth is small for a jack and the forehead runs in a gentle curve instead of dropping steeply, and several of them trail long filaments from the front of the dorsal and anal fins when young, losing them as they grow.

Barcheek Trevally

Carangoides plagiotaenia

Blue Trevally

Carangoides ferdau

Coastal Trevally

Carangoides coeruleopinnatus

Longfin Trevally

Carangoides armatus

Orangespotted Trevally

Carangoides bajad

PoisonousLC

Yellowspotted Trevally

Carangoides fulvoguttatus

Caranx

The hunters, and the largest jacks here. Steep blunt forehead, deeply forked tail, and a flank carrying almost no scales at all - just a row of hard bony scutes along the stalk in front of the tail. Several of them flush dark while working a school and pale again once it is over.

Scomberoides

The queenfish. Long, strongly compressed bodies with a row of dark blotches along the flank, and a first dorsal that is not really a fin - a row of short separate spines instead. They work the surface and the shallows rather than the drop-off.

Doublespotted Queenfish

Scomberoides lysan

Needlescaled Queenfish

Scomberoides tol

VenomousLC

Talang Queenfish

Scomberoides commersonnianus

Trachinotus

Pompanos and darts, built for moving water: deep compressed bodies, sickle-shaped fins, blunt snouts, and a life spent in the wash and over open sand rather than out along the drop-off. What they do there splits the genus - one of the two here crushes shellfish with a toothless mouth, the other hunts small fish inside the surf line.