Elagatis bipinnulata

Elagatis bipinnulata

The rainbow runner also known as the rainbow yellowtail or Hawaiian salmon (Elagatis bipinnulata, Quoy & Gaimard, 1825) is a marine bony fish of the Carangidae family.

Systematics –
Domain Eukaryota,
Kingdom Animalia,
Phylum Chordata,
Class Actinopterygii,
Order Carangiformes,
Family Carangidae,
Genus Elagatis,
Species E. bipinnulata.
The following terms are synonymous:
– Egalatis bipinnulatus (Quoy & Gaimard, 1825);
– Elagatis bipinnulatus (Quoy & Gaimard, 1825);
– Elegatis bipinnulata (Quoy & Gaimard, 1825);
– Elegatis bipinnulatus (Quoy & Gaimard, 1825);
– Elegatis bipunnulata (Quoy & Gaimard, 1825);
– Elegatus bipinnulatus (Quoy & Gaimard, 1825);
– Micropteryx bipinnulatus (Quoy & Gaimard, 1825);
– Seriola bipinnulata Quoy & Gaimard, 1825;
– Seriolichthys bipinnulatus (Quoy & Gaimard, 1825);
– Elagatis bipinnulatus Bennett, 1840;
– Irex americanus Valenciennes, 1862;
– Irex indicus Valenciennes, 1862;
– Seriola pinnulata Poey, 1860;
– Seriolichthys lineolatus Day, 1867.

Geographic Distribution and Habitat –
Elagatis bipinnulata is a pelagic fish belonging to the Carangidae family, characterized by a circumtropical distribution, present in tropical and subtropical waters of all the world’s oceans. The species has been reported between approximately 44° north and 41° south latitude, making it one of the most widespread pelagic species in the tropics.
In the western Atlantic Ocean, it ranges from Massachusetts and Bermuda to the northeastern coast of Brazil, including the Gulf of Mexico, the Bahamas, and the Greater and Lesser Antilles. In the eastern Atlantic, it reaches at least the Azores.
In the Pacific, it is widely distributed in both the western and eastern Pacific, while in the Indian Ocean, it is slightly less common and is rare or absent in the Persian Gulf.
In the Mediterranean Sea, it is an occasional presence, generally as a Lessepsian migrant through the Suez Canal, without having yet established stable populations. Records have also come from the Canary Islands.
The species is classified as reef-associated, despite being predominantly pelagic. It lives primarily in surface waters up to approximately 150–164 meters deep, being most common between the surface and the first 50 meters.
Adults frequent the open sea but can approach the coast, especially near coral reefs, submerged reefs, continental shelves, and oceanic islets.
They occasionally enter coastal lagoons, while juveniles may also temporarily enter estuaries.
Like many other pelagic jackfish, this species displays a strong attraction to any floating object, natural or artificial. It is frequently observed under logs, large masses of floating Sargassum, and especially near Fish Aggregating Devices (FADs), artificial structures used in ocean fishing. Studies have shown that individuals typically occupy a water volume of approximately 12 meters in depth and a 10-meter radius around such structures, using them as permanent landmarks.

Description –
Elagatis bipinnulata is the only species belonging to the genus Elagatis, established in 1840 by Frederick Debell Bennett. Phylogenetically, it represents one of the most primitive members of the Naucratini tribe and is closely related to fish of the Seriola genus.
Unlike most Carangidae, which have a tall, laterally compressed body, the rainbow runner has an extremely slender, subcylindrical, and fusiform body, adapted to fast swimming in the open sea.
The head is relatively long, with a pointed snout and a rather small mouth, the posterior margin of which does not reach the eye. The eyes are small and generally have a golden iris.
The dentition consists of minute bands of villiform teeth distributed across the jaws, palate, and tongue.
The species has two dorsal fins; the first usually has six spines (about 4% of individuals have only five); The second consists of one spine and 25–30 soft rays, ending in two separate rays that form a fin; an anal fin with a single anterior spine, followed by one spine and 18–22 soft rays, also ending in a fin; relatively short, non-falcate pectoral fins; ventral fins with one spine and five soft rays; and a deeply forked caudal fin, particularly developed for high-speed swimming.
The lateral line has a weak anterior curvature, completely lacks the bony scutes typical of other Carangidae, and is made up of approximately 100 scales. The skeleton comprises 24 vertebrae.
Identification of the species is facilitated by its highly distinctive coloration.
The back varies from olive blue to deep green, gradually fading to a silvery white belly.
Along each flank are two thin light blue or bluish-white bands; a broad central olive-yellow band.
This color combination is the origin of the common name “Rainbow Runner.”
The maximum reported length varies between 107 and 120 cm, although some sources exceptionally cite individuals up to 180 cm. The maximum documented weight is 46.2 kg.
The extremely streamlined body shape is one of the best adaptations among the Carangidae to pelagic life, allowing for long distances and high speeds.

Biology –
Elagatis bipinnulata is a highly gregarious fish, forming schools of a few individuals up to several hundred individuals.
It is also a highly migratory species, adapted to life in constant motion in ocean waters.
Biochemical analyses have shown that its musculature contains unusually high concentrations of docosahexaenoic acid (DHA), a characteristic shared with other large migratory fish such as tuna and likely related to the need to sustain continuous swimming activity.
It is an extremely fast carnivorous predator.
The diet primarily comprises small pelagic fish, cephalopods, shrimp, small crabs, and numerous planktonic crustaceans.
Pacific populations show a marked preference for the small jackfish Decapterus macarellus, even when other prey is abundant.
Both swimming ability and prey hunting efficiency rapidly increase as they grow.
The species is also one of the few pelagic fish known to regularly feed on marine insects of the genus Halobates, ocean skaters that live on the surface of the sea.
Sexual maturity is reached at about 60 cm in fork length. Reproduction varies significantly with water temperature. In the Atlantic, it occurs mainly from spring to early autumn.
In tropical waters above 27°C, however, spawning can occur year-round, although seasonal peaks are observed, as observed in the western Pacific in the months of May and between December and January.
The species is oviparous, with eggs and larvae that are completely pelagic.
The larvae possess a distinctive supraoccipital crest and pigmentation that facilitates recognition.
Growth is relatively rapid: 30 cm in the first year; 46 cm in the second; 59 cm in the third; 69 cm in the fourth; and 77 cm in the fifth.
Juvenile migrations are still poorly understood.
The fry are frequently observed associated with large floating mats of Sargassum, which simultaneously offer refuge from predators and an abundance of small organisms to feed on.

Ecological Role –
The rainbow runner occupies an intermediate position in the food web of tropical pelagic ecosystems.
As a predator, it helps control the populations of small pelagic fish, cephalopods, planktonic crustaceans, and surface-dwelling marine insects.
In turn, it constitutes an important prey for numerous large ocean predators.
Among those documented are the Fraser’s dolphin (Lagenodelphis hosei), numerous species of seabirds belonging to the Laridae family, and large predatory fish and pelagic sharks.
Its habit of aggregating around FADs, floating logs, and Sargassum mats contributes to the formation of complex pelagic communities, in which the rainbow runner plays an important role in the transfer of energy between the lower and upper levels of the food web.
From an anthropogenic perspective, although it is not a primary target species like tuna or amberjack, it is frequently caught as bycatch in industrial tuna and shark fisheries.
Bycatch is typically sold fresh, frozen, or salted.
The species is also highly prized in sport fishing, thanks to its remarkable strength and speed during the fight, and is also used as live or dead bait in deep-sea fishing for large pelagic fish such as marlin, sailfish, and tuna.

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.picture-worl.org/actinopterygien-nouvelle-caledonie-3-elagatis-bipinnulata-quoy-gaimard-18252.html