Jacks, Amberjacks, PompanosCarangidae

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.