The rainbow runner, belonging to the Carangidae family, is the sole member of the Elagatis genus. Initially described by French zoologists Jean René Constant Quoy and Joseph Paul Gaimard in 1825, the species was originally named Seriola bipinnulata due to its perceived relationship with amberjacks. Subsequent taxonomic revisions led to the creation of the Elagatis genus by Frederick Debell Bennett in 1840. The name "rainbow runner" refers to the stunning coloration exhibited by this species, which sets it apart from its relatives.
Rainbow runners possess a unique body shape within the jack family, characterized by a subcylindrical and elongated structure. Their pointed head and snout taper towards a distinct rear end, from which the caudal fin emerges. Notable features include relatively small eyes, villiform bands of teeth on the jaws, and minute teeth on the roof of the mouth and tongue. The species boasts two dorsal fins, with the second finlet separated from the long second ray. The anal fin consists of a detached spine anteriorally, accompanied by a main fin and a finlet. While the dorsal and anal fins are relatively low, the dorsal fin is notably longer than the anal fin. The pectoral fin, comparable in size to the pelvic fin, lacks a falcate shape. Rainbow runners exhibit a striking coloration, with a dark olive blue to green upper body that transitions to white underneath. Longitudinal light blue to bluish white stripes run along the sides, with an olive to yellow stripe between them.
Rainbow runners are found in tropical and subtropical waters across the globe, inhabiting both coastal and offshore regions. In the Western Atlantic, their range extends from Massachusetts and Bermuda to northeastern Brazil, encompassing the Gulf of Mexico, the Bahamas, and the Greater and Lesser Antilles. The species is widely distributed throughout the Pacific Ocean, with sporadic presence in the Indian Ocean. While they occasionally visit the Mediterranean Sea through the Suez Canal, rainbow runners have not established permanent residency there. These pelagic fish exhibit versatility in their habitat choices, often venturing near shorelines, lagoons, and even estuary systems. They are also attracted to fish-attracting devices (FADs) deployed in open waters.
Rainbow runners are known for forming schools of various sizes, ranging from small groups to large aggregations. Their highly migratory behavior is accompanied by adaptations such as high levels of docosahexaenoic acid in their muscles, which aids in efficient swimming and prey-searching abilities. As carnivores, rainbow runners have a diverse diet that includes small fish, cephalopods, and pelagic crustaceans such as shrimp and crabs. They exhibit selectivity in prey choice, with regional variations in preferred food sources. Rainbow runners also play a crucial role in the food chain, serving as prey for larger species such as Fraser's dolphins and certain seabirds.
The size at sexual maturity is known to be around 600 mm in fork length for females, while estimates for males range between 600 and 650 mm. In the Atlantic, spawning occurs from spring to early autumn, although populations in warmer waters exhibit year-round spawning with seasonal peaks. Rainbow runners are oviparous, producing pelagic eggs and larvae. Their larval stages have been extensively studied, revealing distinctive features such as a supraoccupital crest and unique patterns of pigment and melanophores. Growth patterns indicate that rainbow runners reach lengths of 30, 46, 59, 69, and 77 cm at 1, 2, 3, 4, and 5 years of age, respectively. While the migration patterns of juveniles are not well-documented, some evidence suggests a migration from equatorial spawning grounds to the coasts of Japan, often floating amidst Sargassum mats.