Black Jack

The Black Jack, also called the Black Trevally, is a large reef-associated jack in the family Carangidae. It is placed in the genus Caranx, alongside other robust, fast-swimming trevallies. Black Jack are found circumtropically around offshore reefs, seamounts, and drop-offs in the Indian, Pacific, and Atlantic Oceans. They are among the darkest-colored jacks, a trait that gives the species its name. Black Jack are considered a widespread and relatively common species in areas with strong currents and steep reef structure. Their broad distribution and habit of forming large schools around offshore pinnacles make them a notable component of tropical reef fish communities worldwide.

Black Jack are a robust, deep-bodied jack with a distinctly dark coloration.

• Color: uniform dark grey to blackish-brown body, darkening further with age and size
• Body shape: deep, laterally compressed, oval profile typical of Caranx
• Fins: dark, sometimes blackish fins including a strongly forked tail
• Head: blunt, steep forehead with a moderately large mouth
• Scutes: prominent bony scutes along the rear lateral line

Compared to other dark jacks, Black Jack lack the bright yellow fin tinges seen in some relatives and are generally the darkest overall of the common reef Caranx species, especially in larger individuals found around deep drop-offs.

Black Jack occur circumtropically in the Indian, Pacific, and Atlantic Oceans, typically around offshore coral reefs, seamounts, and steep drop-offs rather than shallow lagoons. They favor areas with strong currents at depths from roughly 3 to 350 meters, often congregating near reef edges and current-swept channels. Adults are more common in deeper offshore reef zones, while juveniles may occasionally use shallower nearshore reef habitat. The species prefers clear tropical water and structurally complex reef terrain that supports the schools of smaller fish it feeds on.

Black Jack often form large, tightly packed schools around offshore reefs, seamounts, and current-exposed drop-offs, a behavior less common in some other trevally species. They are active, fast-swimming predators that hunt small fish and squid, frequently patrolling reef edges where currents concentrate prey. Schooling likely offers protection from larger predators such as sharks, which are commonly seen shadowing Black Jack aggregations. Spawning behavior in the wild is not well documented but is presumed to involve pelagic egg release, consistent with other carangids. As mid-to-upper trophic level predators, Black Jack play a role in structuring reef fish communities.