The Bar jack (scientific name: Carangoides ruber) is a member of the jack family (Family Carangidae) that lives on coral reefs in the Western Atlantic Ocean and the Caribbean Sea.

Bar jack. Source: ''Reef Fish Identification'', New World Publications © 1994

Scientific Classification Kingdom: Animalia (Animals) Phylum:--- Chordata Class:------ Osteichthyes (Bony Fishes) Order:-------- Perciformes Family:-------- Carangidae (Jacks) Genus:----------Carangoides Species:----------Carangoides ruber (Bloch, 1793)

Physical Description

Bar jacks are streamlined silvery fish that range in length tfrom 20 to 69 millimeters and weigh up to 7.9 kilograms. The species derives its name from the black bar that runs along the border of the back and dorsal fins to the lower tail fin. This fish can change color from silvery to black.

Distribution

C.ruber is found in the Western Atlantic from New Jersey (USA), Bermuda, and Gulf of Mexico to southern Brazil and throughout the Caribbean Sea.

Habitat

This species inhabits coral reefs at depths ranging from zero to 35 meters, most commonly from zero to 22 meters.  On occasion, schools of larger fish also occur under large Sargassum, a brown algae, mats. Juveniles may be observed under patches of Sargassum.

Feeding Behavior

Young bar jacks feed on plankton near the surface. Adult bar jacks mostly eat fish, but they may also consume invertebrates such as shrimp. Usually, bar jacks feed on fish in the water column and they rely on sight to locate their prey.  They are active pursuit predators that actively attack their prey.

In addition,  bar jacks can feed on the bottom, sometimes while following stingrays or goatfishes and eating food stirred up by the bottom feeders. Bar jacks often change to a darker coloration when feeding near the bottom.

Behavior

Bar jacks usually live in clear, shallow waters over coral reefs. They are typically found in schools varying in size from a few fish to many, but occasionally they may swim alone.

Reproduction

Most spawning occurs in offshore waters between the months of February and August. Fish gather in spawning groups number in the hundreds to spawn. Spawning occurs in the water column where the up to 230,000 eggs released by the female are fertilized.   Larvae enter the pelagic stage after the eggs hatch.  Juveniles may hide beneath  floating pelagic Sargassum mats. Young fish often inhabit the shallow reef waters, but move offshore once they reach sexual maturity at around 24 centimeters in length.

Juveniles are commonly found in the Gulf Stream Current during late April through November, reaching maximum numbers in May to August.

Associations

Bar jacks may forage in tandem with bottom feeders such as stingrays and goatfishes.

Conservation Status

The bar jack is not deemed to be a species at risk.

References and Further Reading

• Encyclopedia of Life. 2011. Carangoides ruber (Bloch, 1793)
• Florida Museum of Natural History. 2010. Bar Jack
• Humann, P. and N. Deloach (Editor), 1994. Reef Fish Identification: Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348078
• Deloach, N. 1999. Reef Fish Behavior, Florida, Caribbean, Bahamas. New World Publications, Inc. Jacksonville, FL. ISBN: 1878348280