The bar jack is a species of fish that lives primarily in the coral reefs of the Southern Gulf of Mexico. It is also found in the Atlantic Ocean off the coast of the Eastern United States as far north as New Jersey. Bar jacks are identified and named for the black bar stripe that runs along their back from their heads to their bottom tail fin. The fish are hunted for sport and food, and most are consumed in the Bahamas.
Beyond the distinctive black bar, the body of a bar jack is mostly silver and gray in appearance, and the underside of the fish is near white in coloration. The fish have been known to also have a bright blue stripe directly underneath the black bar, and because of this are also called the blue-striped cavalla. A bar jack has a scaled chest, forked tail, and its fins are longer in length than its head. Length-wise, the fish reach around 19.7 inches (50 cm), and weigh in at around 18 pounds (8.2 kg).
Bar jacks are found concentrated around the Bahamas and the West Indies, and move back and forth between large coral reefs in the region. They can be easily seen by scuba divers in the area and are also frequently caught by sports fisherman. The bar jack is eaten routinely in the Bahamas region, but caution is advised because it has been known to cause cases of Ciguatera poisoning. This is result of a toxin the fish pick up from the coral reefs which is spread by dinoflagellates.
Juvenile bar jacks do have the full black bar along their backs, and instead have a broken segmented black stripe. Once they reach maturity, the full black bar develops. Young bar jacks also do not hunt in the same way as adults, and instead depend on scavenging and bottom-feeding. A juvenile bar jack follows around larger fish, such as stingrays, and eats from their debris. The immature fish also eat zoo plankton found floating near the water's surface.
Adult bar jacks eat smaller fish and invertebrates such as shrimp. They hunt only during they day, and have almost no nocturnal activity. Bar jacks have a full set of teeth, with two rows on top, and one row on bottom. They are not listed as a threatened or endangered species. The fish are eaten by dolphins and other predators, such as the king mackerel, the cero mackerel, and the greater amber-jack.