Caranx hippos
Caranx hippos
The crevalle jack or common jack, black-tailed trevally, couvalli jack, black cavalli, jack crevale, yellow cavalli (Caranx hippos, Linnaeus, 1766) is a bony fish belonging to the Carangidae family.
Systematics –
Domain Eukaryota,
Kingdom Animalia,
Phylum Chordata,
Class Actinopterygii,
Order Carangiformes,
Family Carangidae,
Genus Caranx,
Species C. hippos.
The following terms are synonymous:
– Scomber hippos Linnaeus, 1766;
– Carangus hippos (Linnaeus, 1766);
– Caranx hippos hippos (Linnaeus, 1766);
– Scomber carangus Bloch, 1793;
– Caranx carangus (Bloch, 1793);
– Caranx carangua Lacepède, 1801;
– Caranx erythrurus Lacepède, 1801;
– Caranx antilliarum Bennett, 1840;
– Caranx defensor DeKay, 1842;
– Trachurus cordyla Gronow, 1854;
– Carangus esculentus Girard, 1859;
– Caranx esculentus (Girard, 1859);
– Caranx hippos caninus Günther, 1867;
– Caranx hippos tropicus Nichols, 1920.
Geographical distribution and habitat –
The Caranx hippos is a large predatory fish belonging to the Carangidae family. It is a species typical of tropical and subtropical waters of the Atlantic, where it lives primarily along the continental shelf. Agile, fast, and powerful, it spends much of its life on the move, often gathered in large schools, but larger adults can become solitary. This fish is found primarily in the Atlantic Ocean, both western and eastern. To the west of the Atlantic, its range includes the coasts of North and Central America, the Gulf of Mexico, the Caribbean, and reaches as far north as Uruguay. Toward the north, it can reach the waters of Nova Scotia, Canada. On the eastern side of the ocean, it is present along the coasts of West Africa, from Senegal and surrounding regions to Angola, and has also been recorded on some Atlantic islands.
The situation in the Mediterranean is more complex. Records, including those from Italy, describe the species as present in the basin, but FishBase considers the Mediterranean to be excluded from the species’ main range. Therefore, in the Mediterranean, it is more prudent to speak of occasional or rare records rather than of a stable and abundant presence.
The horse trevally is primarily a fish of the neritic zone, that is, the marine waters above the continental shelf. It can live from the coastal strip to the open sea, generally between 1 and 200 meters deep, although adults can reach depths of about 350 meters.
Its habitat is highly diverse. Juveniles often frequent estuaries, lagoons, seagrass beds, and shallow coastal areas, where they find an abundance of small prey and favorable conditions for growth. They can also tolerate brackish water and penetrate the lower reaches of rivers. Adults, however, tend to gradually move toward deeper waters and offshore environments, including reef zones and the edges of the continental shelf.
This ability to utilize very different environments during the various life stages is one of the most interesting ecological characteristics of the species.
Description –
The Caranx hippos is a robust and muscular fish, built for fast swimming and chasing. Its body is elongated and moderately compressed laterally, while its head has a rather steep profile. The eyes are protected by a characteristic adipose eyelid, common among jackfish.
It is one of the largest members of the Caranx genus: it can reach approximately 124 cm in total length and 32 kg in weight, although exceptionally large individuals are much less common. Its normal length is considerably shorter.
The shape of its fins immediately reveals its lifestyle. The falcate pectoral fins and the powerful, forked caudal fin allow the fish to make sudden accelerations and changes of direction while hunting. The lateral line is characterized by numerous bony scutes, while the thorax is almost scaleless.
Its coloration helps make it easily recognizable. The back can be olive-green, greenish, or bluish, while the sides are silvery, sometimes with golden highlights. The dark spots in the operculum region and near the pectoral fins are particularly distinctive. The caudal fin often has yellowish hues.
Juveniles have an even different appearance: approximately five dark vertical bands appear on the sides, a pattern that tends to disappear as they grow.
Biology –
The horse trevally is a diurnal predator and spends much of the day foraging. Its diet is dominated by fish, especially when it reaches adult size, but also includes shrimp, other crustaceans, squid, and various marine invertebrates.
Its diet varies throughout its life. Juveniles may feed heavily on crustaceans and small prey, while as they grow, their consumption of fish increases. Adults are more opportunistic predators and can exploit the most abundant prey available in the environment.
The species is generally gregarious: especially during juvenile stages and for most of its life, it forms large, fast-moving schools. As it grows, however, some individuals become more solitary and frequent deeper areas.
Reproduction is particularly interesting. Adults can gather in large breeding aggregations, which in some areas can number up to a thousand individuals. Within the group, pairs form, which temporarily separate from the school to lay and fertilize their eggs.
Reproduction can occur year-round, although periods of increased activity have been observed in various regions. The eggs are pelagic, meaning they remain suspended in the water column and are carried by currents. The eggs described in the notes have a diameter of approximately 0.7-0.9 mm.
The larvae also initially lead a pelagic life. The young can use floating objects and large accumulations of Sargassum as shelter and later reach coastal areas. Estuaries and seagrass meadows represent important nursery areas, where the young can find food and protection.
Growth is relatively rapid, and the species can reach a lifespan of approximately 17 years, according to the studies reported in the notes.
A curious behavior involves the ability to produce sounds similar to grunts or growls. These sounds have been observed especially when the fish is caught and handled.
The horse trevally is also of considerable importance to humans. It is targeted by both commercial and recreational fisheries and is considered a hard-fighting gamefish. Catches are made using various fishing methods, from nets to hooks and trolling lines.
Ecological role –
Within marine ecosystems, the horse trevally primarily plays the role of a medium- to high-trophic level predator. Its predominantly fish-based diet allows it to directly influence the abundance and distribution of small fish species, as well as crustaceans and other invertebrates. FishBase estimates the species’ trophic level at around 3.6, consistent with its role as a carnivorous predator.
However, its importance is not limited to predation. The life cycle of the horse trevally connects different environments: juveniles utilize estuaries, lagoons, and submerged meadows, while adults can move to the deeper waters of the continental shelf. The species thus contributes to the transfer of energy between coastal and marine ecosystems.
The horse trevally is also part of a complex food web. While an effective predator as an adult, it can be preyed upon by larger marine predators, while eggs and juveniles are exposed to predation by numerous organisms.
Their presence in large schools is therefore an important element of ecosystem dynamics: thousands of individuals can temporarily concentrate in certain areas to feed or reproduce, making these aggregations particularly significant for the functioning of the food web.
Despite intense fishing pressure, the horse trevally is currently classified by the IUCN Red List as “Least Concern”; FishBase reports this assessment as the global one, with an assessment date of September 10, 2018. This does not mean that individual populations are free of problems: fishing pressure and changes in coastal habitats can still be important factors to monitor.
The horse trevally is therefore an example of a large coastal predator capable of adapting to different environments and exploiting a wide variety of resources. Its lifespan, from the estuary of juveniles to the deeper waters of adulthood, clearly demonstrates how closely interconnected the different marine environments are.
Guido Bissanti
Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Louisy P., 2016. Guide to the identification of marine fish of Europe and the Mediterranean. Il Castello Editore, Milan.
Photo source:
– https://www.auxbulles.com/explore-sealife-fish_crevalle_jack_caranx_hippos.html