The species reaches sexual maturity at between 225 and 280 mm across its range, with spawning occurring offshore year round, although this peaks during the warmer months.

There has been some suggestion that the eastern Pacific species Caranx caballus, the green jack, may be conspecific with C. crysos, although this currently remains unresolved.

[2] The species was first scientifically described by the American ichthyologist Samuel L. Mitchill in 1815, based on a specimen taken from the waters of New York Bay, USA which was designated to be the holotype.

[4][6] There have been suggestions that the blue runner may be conspecific with the eastern Pacific species Caranx caballus (green jack), although no specific studies have been undertaken to examine this relationship.

[4] The blue runner is morphologically similar to a number of other carangids, having an elongated, moderately compressed body with dorsal and ventral profiles of approximately equal convexity and a slightly pointed snout.

[citation needed] In the eastern Atlantic the southernmost record is from Angola, with the blue runner distributed extensively along the west African coast up to Morocco and into the Mediterranean Sea.

[16] There has been a trend of having this and other tropical species found further north more often, with publications indicating the blue runner has recently established stable populations in the Canary Islands, where it had been rarely sighted.

Some authors have attributed this northward migration to rising sea surface temperatures, possibly the result of climate change.

Juvenile fish are also known to inhabit the shallow waters of inshore lagoons, taking refuge around mangroves[10] or in seagrass amongst coral reef patches.

[19] Blue runner are easily attracted to any large underwater or floating device, either natural or man made.

[20] In these situations, blue runner always form small aggregations at the water surface, while other larger species tend to congregate slightly deeper.

[21] Purpose-built artificial reefs[22] and marine aquaculture cage structures are also known to attract the species, with the former having the added benefit of dispersing wayward food scraps.

[citation needed] The blue runner is a fast-swimming predator which primarily takes small benthic fishes as prey in inshore waters.

A Puerto Rican study found the species supplements its fish dominated diet with crabs, shrimps, copepods and other small crustaceans.

[25] More detailed research in Cape Verde found as well as fish, blue runner take shrimp, prawns, lobsters, jellyfish and other small invertebrates.

[27] Adult blue runner living offshore or aggregating around oil and gas platforms tend to have less fish in their diet, foraging extensively on larger zooplankton during the summer months, with larval decapods and stomatopods, hyperiid amphipods, pteropods, and larval and juvenile fishes also taken.

[4][30] The blue runner reaches sexual maturity at slightly different lengths throughout its range, with all such studies occurring in the west Atlantic.

[34] Larvae and small juveniles remain offshore, living either at depths of around 10 to 20 m,[32] or congregating around floating objects, particularly Sargassum mats and large jellyfish.

Artisanal fisheries in Santa Catarina Island have shown blue runner to be third most important and abundant species, making up 5.6% of landings, or 4.38 tonnes.

[11] Blue runner is also of high importance to recreational fisheries, with anglers often taking the species both for food and to use as bait.

It is considered a fairly low-quality table fish,[10] and larger specimens are known to carry the ciguatera toxin in their flesh, with several cases reported from the Virgin Islands.