Rainbow Runner.

The rainbow runner, Elagatis bipinnulata (also known as the rainbow yellowtail, Spanish jack and Hawaiian salmon), is a common species of pelagic marine fish of the jack family, Carangidae. The species is widespread throughout the tropical and subtropical waters of the world, inhabiting both coastal as well as far offshore areas. The species is the only member of the genus Elagatis, which was created 15 years after its initial description, and is closely related to the amberjacks. The rainbow runner is easily distinguished by its body shape, and the brilliant colouration which gives the fish its name. It is a fast swimming predator, taking small fish, cephalopods and a wide variety of planktonic crustaceans. The species reaches sexual maturity at around 60 cm (24 in), and spawning takes place at different times, with some populations spawning year round, while others only spawn at certain times of the year. The species is a well known game fish, taken by a variety of fishing methods and is a well rated table fish. Large amounts of the species are taken as bycatch in tuna and shark fishing operations and marketed.

Taxonomy and naming

The rainbow runner is the only species in the monotypic genus Elagatis, which is one of thirty genera in the jack family, Carangidae. The Carangidae are Perciform fishes in the suborder Percoidei. The species was first scientifically described in 1825 by French zoologists Jean René Constant Quoy and Joseph Paul Gaimard based on the type specimen collected from the Indian Ocean, somewhere in the Malay Archipelago. They named the species Seriola bipinnulata, believing the species was related to the amberjacks. This was later revised to the genus Seriolichthys by Bleeker before it was concluded the species warranted a new genus. The genus Micropteryx was initially created, but was already in use in the Lepidoptera. In 1840, Edward Bennett was recognized as the author of the genus Elagatis, taken from a name published in a whaling voyage memoir, which he used in combination with the species name of bipinnulatus, which was deemed to be incorrect and the original spelling of bipinnulata reinstalled. Phylogenetically, the species is most closely related to the amberjack genus, Seriola, being the most basal member identified of the carangid subfamily Naucratini. This has been determined by the sequencing of the mitochondrial cytochrome b genome, as well as older morphological studies.
The species wide range has led to a wide array of local common names, with the most common English name being 'rainbow runner' in reference to its colouring. Other names frequently applied include rainbow yellowtail, Hawaiian salmon, Salmon (incorrectly), Spanish Jack, as well as over twenty other names in various languages.

Description

The rainbow runner has a body that is atypical of the jack family, which generally have deep, compressed bodies. The rainbow runner has a subcylindrical, elongated to almost fusiform body, with a long pointed head and snout and a tapering rear end before the caudal fin emerges. The eye is relatively small and the teeth are arranged on jaws in villiform bands, with minute teeth also present on the roof of the mouth and tongue. The fish has two dorsal fins, although the posterior rays of the long second fin have separated into a finlet. The first dorsal consists of 6 spines, the second of a single spine and 25 to 30 soft rays, with the last two as a separate finlet. Approximately 4% of rainbow runner have only five spines in the first dorsal fin, and are apparently born without them. The anal fin consists of one spine detached from the fin anteriorally, while the main fin has a single spine and 18 to 22 soft rays, with the last two detached to form a finlet like the dorsal fin. The dorsal and anal fins are quite low, and the dorsal fin is much longer than the anal. The pectoral fin is small for a carangid, about the length of the pelvic fin and is non-falcate with 20 rays. The pelvic fin consists of one spine and five branched soft rays. The caudal fin is also highly diagnostic, being deeply forked and consisting of 17 caudal rays, 9 dorsally and 8 ventrally. The lateral line has a slight anterior arch and there are no scutes present on the line, but possesses about 100 scales. The scales covering the body and parts of the operculum, cheek, pectoral fins, pelvic fins, and caudal fins are ctenoid in shape. The species has 24 vertebrae.
The colour of the fish is possibly the easiest way to identify the rainbow runner, with the name taken from the species striking colours. The upper body is a dark olive blue to green and fading to white underneath. There are two narrow light blue to bluish white stripes running longitudinally along the sides, with a broader olive to yellow stripe between them. The maximum length of the species is somewhat contentious, with most sources giving a known maximum length of between 107 cm (42 in) and 120 cm (47 in) cm, while one source asserts the species reaches 180 cm (71 in) cm in length. The maximum known weight is confidently known to be 46.2 kg, as recorded by the IGFA.