Fish Facts » Jack Crevalle
Description
The crevalle jack has a body depth of about three times its fork length. It has large eyes. The chest is scaleless except for a small patch of scales in front of the pelvic fins. This patch is apparent by the time the fish reaches a fork length of 0.98 inches (2.5 cm). The crevalle jack is the only jack in the western Atlantic Ocean with this patch of scales. There is an oval black spot on the pectoral fins; this appears at about 4.72 inches (12.0 cm). Between the seventh and the eighth spines of the adult there is an overgrowth of skin. The two most distinguishable features of this fish are the patch of scales between the pelvic fins and the oval, black spot on the pectoral fins. The crevalle jack is greenish-bluish or bluish-black above and silvery white to yellowish or golden below. This serves to blend in with the water from a predator searching from above, and to blend with the sunlight from a predator hunting from below. There is an oval, black spot on the pectoral fins. Juveniles have 5 dark bars on their bodies. These black bars are present until the fish reaches a size of 6.46 inches (16.4 cm). There is an area of dark pigment above the peduncle that appears at 1.18 in. (3.0 cm) and is very dark once the fish reaches a size greater that 3.94 inches (10.0 cm) in length. The juvenile has pigment spots on the anal spines and membranes, which disappear by the time its size reaches 1.38 inches (3.5 cm). The pelvic fin remains unpigmented after 0.79 inches (20 mm) and at about 1.18 inches (3.0 cm) the pigment of the caudal fins develops. The coloration of the juvenile holds between 0.79-1.57 inches (2.0-4.0 cm) and fades between 1.57-1.97 inches (4.0-5.0 cm).
Habitat
The crevalle jack is found in oceanic, estuarine or riverine environments. This is influenced by the life stage of the fish. They primarily are found along the continental shelf, but occur in waters as deep as 327 feet (100 m). Fish found in these deep waters are usually larger individuals. Larval and juvenile jack crevalles are found in upstream currents and are common in shallow brackish waters. Adults, on the other hand, usually occupy upstream currents, reefs, offshore areas or shallow inshore areas. Jack crevalles live in a variety of temperatures and salinities. Adults usually inhabit areas with temperatures between 64-92.5°F (18-33.6ºC) of water and larvae are found in areas with temperatures between 69-84.9°F (20.4-29.4ºC) of water. Crevalle jacks have been found in fresh water to salt water environments, depending on life stage. Larvae have been collected in areas with salinities between 35.2-36.7 parts per thousand (ppt). Adults have been found in freshwater habitats as well as those with a salinity of 43.8 ppt. They are most commonly found at salinity above 30 ppt. The crevalle jack is a pelagic fish. Both adults and juveniles are usually found in schools. However, larger individuals may be found swimming the waters alone.
Diet
The crevalle jack is a diurnal predator. Adults prey upon on a variety of fish, shrimp and invertebrates. Juveniles feed mainly on small fish and crustaceans.
Fishery
Although the crevalle jack is a relevantly unimportant commercial fish, it is fished commercially throughout the year in southwest Florida, and in the spring, fall, and summer in the Gulf of Mexico. It is an important sport fish, and is exploited throughout its range.
Size
The maximum size of a crevalle jack is 39.8 inches (101 cm) and 55.1 pounds (25 kg), however they are common to 23.6 inches (60 cm). After the juvenile reaches a size of 1.97 inches (5.0 cm), its growth rate increases. Females are typically larger than males.
Range
The crevalle jack's range consists mainly of the coastal areas of the western Atlantic Ocean from Novia Scotia to Uruguay. They also often are found throughout the Gulf of Mexico, especially along the coast of Texas and the west coast of Florida.
Source(s)
Florida Museum of Natural History
Source(s) on the web
http://www.flmnh.ufl.edu/fish/Gallery/Descript/CrevalleJack/CrevalleJack.html