Jackfish. School of jackfish or big-eye trevally, Caranx sexfasciatus, silhouetted against the sun. These fish congregate in large schools during the day, seeking safety in numbers from predators. The resulting wall of fast-moving fish makes it difficult for a predator to focus on a single target. At night the school fragments to feed, mainly on smaller fish. Jackfish are fast- swimming predators reaching lengths of 80 centimetres. They inhabit tropical and subtropical coastal waters near reefs. They are regarded as an excellent food fish.