Bigeye trevally

The bigeye trevally is classified within the genus Caranx, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae, which in turn is part of the order Carangiformes. Prior to its description in 1825, the species was often confused with the similar-looking Atlantic species Caranx hippos, and its synonym Caranx carangus. The species was first properly scientifically described by the French naturalists Jean René Constant Quoy and Joseph Paul Gaimard in 1825 from a specimen collected off Waigeo, Indonesia which was designated to be the holotype. They named the species Caranx sexfasciatus which the species is still currently accepted as, with the specific epithet meaning 'six banded' in relation to its juvenile colouration. Following this, the species was independently redescribed and named around fifteen times, and incorrectly broken into two subspecies. In his massive ichthyological volume entitled Histoire Naturelle des Poissons, Georges Cuvier managed to assign no less than four junior synonyms to the species, while the most recent renaming was by Yojiro Wakiya in 1924, who applied the name Caranx oshimai. The two subspecies proposed were Caranx sexfaciatus elacate and Caranx sexfaciatus marginatus, both based on prior descriptions by Jordan and Evermann, and Gill respectively. All names except Caranx sexfasciatus are considered junior synonyms under ICZN rules and discarded. The common name preferred by most authorities is 'bigeye trevally', 'bigeye kingfish', 'bigeye crevalle jack' or bigeye jack', with other names used including 'great trevally', 'six-banded trevally' and 'dusky jack'. ==Distribution and habitat==

, Australia The bigeye trevally is widely distributed throughout the tropical and subtropical waters of both the Indian and Pacific Oceans. in this central Indo-pacific region. In the Pacific Ocean, the bigeye trevally inhabits most of the tropical island groups including Hawaii, with its range extending east to the western American coastline. In this eastern region of its distribution it has been recorded from the American state of California in the north, including the Gulf of California, and south to Ecuador and the Galapagos Islands. Those that live offshore often live on deeper seamounts or reefs around offshore islands. The species moves with the tide in some regions, entering shallow lagoonal areas as the tide rises, and moving back to the deeper reefs as it retreats. and even estuaries. Juvenile bigeye trevally have been reported in rivers from several locations, and are known to penetrate well into the upper reaches of rivers. As the fish grows, it moves back to deeper waters over reefs. The species has been reported in pelagic open ocean settings, milling around stationary buoys, indicating the species may follow floating debris far out to sea. ==Description==

, at Norfolk Island The bigeye trevally is one of the larger members of Caranx, growing to a maximum recorded size of 120 cm in length and 18.0 kg in weight. The dorsal fin is in two distinct sections; the first consisting of 8 spine and the second of 1 spine and 19 to 22 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 14 to 17 soft rays. The pelvic fins consists of 1 spine and 17 to 18 soft rays, while the caudal fin is strongly forked and the pectoral fin falcate. The species lateral line is moderately arched anteriorly, with 49 to 50 scales in this section, while the straight section contains 0 to 3 scales and 27 to 36 strong scutes. The breast is completely covered in scales. The species has well-developed adipose eyelids, while its dentition consists of an outer row of widely spaced canine teeth and an inner band of villiform teeth in the upper jaw, with a row of widely spaced conical teeth on the lower jaw. The bigeye trevally has 21 to 25 gill rakers and 25 vertebrae. and the dorsal colour is a silvery olive to blue green, fading to silvery white below. In juveniles, the fins are pale grey to yellow with darker edges, becoming darker overall in adulthood, with the anal and caudal fins yellow to black and the second dorsal fin olive to black. The tip of the second dorsal fin has a distinctive white tip. The bigeye trevally also has a small dark opercular spot on the upper margin. ==Biology==

The bigeye trevally is a schooling species, known to form aggregations consisting of more than 1500 fish. The species is often seen in these large schools either stationary or slowly moving around the reef complexes they inhabit during the day. At night, these schools dissolve, and the species become active, taking most of its prey during the nocturnal period. Diet and feeding The bigeye trevally is a fast-swimming predatory species that has had several studies determine its diet in various places throughout its distribution. As mentioned above, the species is mostly inactive during the day, and feeds at dusk and through the night. however supplements its diet with a varied array of invertebrates. These include crustaceans such as shrimps, decapods, copepods and stomatopods, cephalopods, gastropods, jellyfish, sponges and even species of open ocean sea-skater insects. Bigeye trevally were found to be the primary fish predators of these sea-skates, and took far more of these than any other species of carangid. Evidence from South African estuaries indicates there is a shift in the species diet as it grows. Young fish below 200 mm in length take mostly the juveniles of other fish species but still have a significant intake of penaeid shrimps, while fish larger than this take small fish nearly exclusively. Spawning is known to occur between July and September in the east Pacific Fish aggregate in large schools prior to spawning, with pairs breaking off the main aggregation to commence spawning. The pair increase their swimming speed to leave the school, with the fish underneath instantly changing colour to a dark black, with this individual also known to chase off any other individuals that approach the pair. There has been little research into the later stages of growth and their rates. Juveniles are known to inhabit either inshore habitats such as estuaries, with an influx of these small fish after spawning in South Africa, The specimen was initially thought to be a bigeye trevally, however a lack of the black opercular spot, light coloured scutes and a smaller than normal eye led to the specimen being examined in more detail. DNA analysis confirmed a hybrid between C. sexfasciatus and C. melampygus, which has been difficult to explain due to the two species vastly different lifestyles and spawning characteristics. ==Relationship to humans==

The bigeye trevally is of varying importance to both commercial and recreational fisheries throughout its range, with the large school sizes allowing for large catches in some regions. In many regions the species is lumped with other jacks in fishery statistics, and therefore worldwide catch is nearly impossible to estimate. Known recent annual catches include those of Saudi Arabia (615–638 t), It is also of high importance in small artisanal and subsistence fisheries, for which statistics are not kept. Bigeye trevally are taken by a number of methods including hook and line, gill nets, purse seines and various other netting methods. The bigeye trevally is also popular with anglers, with the species rated as an excellent gamefish in larger sizes. The species is commonly taken by boat fishermen over reef complexes, however schools often hang around jetties and wharves, allowing for frantic fishing when the fish are on the bite, especially after dusk. The species is also occasionally taken from beaches, but rarely in large quantities. Common techniques for catching the fish include bait fishing, which can involve both live or dead bit including fish, squid or various crustaceans, or lure fishing. Bigeye trevally are known to accept many lure types including bibbed lures, surface poppers and metal slugs jigged in rapid retrieve from the ocean floor. In larger sizes, gear must be robust and well maintained to land the fish. The IGFA maintains a full set of line class and tippet records for the bigeye jack. The all tackle world record stands at caught off Poivre Island in the Seychelles. The bigeye trevally's edibility is said to range from fair ==References==