Cottonmouth Jack

The Cottonmouth Jack is an unusual, deep-water member of the jack family (Carangidae), named for the pale, whitish interior of its mouth. It has a circumtropical distribution, occurring in the Atlantic, Pacific, and Indian Oceans, typically over deeper offshore waters along continental shelves and slopes rather than shallow reefs. It belongs to the genus Uraspis, a small group of carangids distinguished by their smooth, elongated bodies and reduced or weakly developed lateral scutes compared to most jacks. Because of its preference for deeper habitats, it is far less frequently encountered than shallow reef-associated jacks, and relatively little is known about its biology, though it carries no specific conservation concern.

• Elongate, moderately compressed, smooth-bodied jack
• Uniform silvery-grey to bluish-grey coloration with little patterning
• Distinctive pale white to cream-colored interior of the mouth, the source of its common name
• Weak or poorly developed lateral scutes compared to typical Caranx jacks
• Blunt, rounded snout profile
• Moderately forked tail

Typically 30-45 cm, up to 70 cm. The plain coloration combined with a pale mouth interior and weakly scuted lateral line are the key features separating it from more common shallow-water jacks.

Cottonmouth Jacks inhabit deeper offshore waters across tropical and subtropical regions of the Atlantic, Pacific, and Indian Oceans, typically occurring along the continental shelf and upper slope at depths of roughly 40-200 m or more. Unlike many reef-associated jacks, they are rarely seen in shallow water and are more characteristic of open, deeper offshore habitats away from coral reef structure. Juveniles may occasionally be found near the surface associated with floating debris before moving into deeper water as they mature. Their circumtropical but deep-water distribution means sightings are infrequent and largely limited to deeper trawl surveys or offshore fishing activity.

Cottonmouth Jacks are among the less-studied carangids due to their deeper-water habits, generally believed to be solitary or loosely aggregated rather than forming the large visible schools typical of shallow reef jacks. They are presumed to be active carnivorous predators, feeding on fish and invertebrates encountered over deeper shelf and slope habitats. Reproductive behavior is poorly documented but likely follows the broadcast-spawning pattern common to the jack family, with pelagic eggs and larvae drifting near the surface before juveniles associate briefly with floating structure. Their deep-water lifestyle limits direct behavioral observation, leaving much of their ecology inferred from related shallow-water carangids.