Yellowstripe scad

The yellowstripe scad, Selaroides leptolepis, (also known as the yellowstripe trevally, yellow-banded trevally, smooth-tailed trevally, slender-scaled trevally and slender trevally) is a species of small inshore fish in the jack and horse mackerel family Carangidae, and the only member of the genus Selaroides. The yellowstripe trevally is distributed throughout the tropical waters of the Indo-West Pacific region, ranging from the Persian Gulf in the west to Vanuatu and New Caledonia in the east. The species is distinguished by its prominent lateral yellow band, and differs from the scads of the genus Selar in having a smaller eye and different dentition. The yellowstripe scad reaches a maximum recorded length of 22 cm, however is normally encountered at sizes less than 15 cm. Phylogenetic studies indicate the yellowstripe scad is closely related to the scads of the genus Selar, although its exact placement in the family Carangidae is less well agreed upon. A schooling species that predominantly inhabits inshore waters, the yellowstripe scad is a predatory fish, taking crustaceans, small fish and a variety of other planktonic prey. Feeding occurs at different times of the day and night throughout its range. The species reaches sexual maturity at around 8–13 cm, with spawning in India shown to occur in two peak periods between January to April and July to October. The yellowstripe scad is an important commercial species, with between 113,000 t and 195,000 t reported worldwide between 1990 and 2010. The species is predominantly harvested with trawls, however is also taken with smaller traditional nets. The yellowstripe scad is marketed fresh, frozen, as a dried fish snack as well as several novel ways including fish powder, surimi and burgers. The yellowstripe scad is the only member of the monotypic genus Selaroides, one of around thirty genera in the jack and horse mackerel family Carangidae. The Carangidae are perciform fish within the subfamily Percoidei. The yellowstripe scad was first scientifically described by the famed French naturalist Georges Cuvier in 1833 based on the holotype specimen taken from the waters of Java, Indonesia. He named the species Caranx leptolepis, with the specific epithet derived from Greek, meaning 'thin scales'. In 1851 the Dutch ichthyologist Pieter Bleeker re-examined the species and concluded it warranted placement in its own genus, which he named Selaroides meaning 'like Selar' in reference to the similarity between these fishes. For unknown reasons Bleeker later reassigned the species to another new genus, Leptaspis, without stating any reason for the change. As Selaroides was published first it has priority according to ICZN rules and Leptaspis is rendered an invalid junior synonym. In the same volume he described Caranx leptolepis, Cuvier also described Caranx mertensii based on a sketch alone. This name is now considered to be synonymous with S. leptolepis. Between 1883 and 1877 the species was redescribed a further three times, with all these names also considered to be junior synonyms. The species is commonly referred to as the 'yellowstripe', 'yellow-banded' or 'gold-banded' scad or trevally in reference to the distinctive yellow strip running along the side of the species. Other names applied to the species include 'smooth-tailed trevally', 'slender-scaled' or 'thin scaled' trevally or scad and 'slender trevally', with an extensive list of non-English names also used. The yellowstripe scad has been included in several phylogenetic analyses of the Carangidae, with each study suggesting slightly different relationships. All studies confirmed its placement in the subfamily Caranginae, a monophyletic grouping including the trevallies, jacks, scads and horse mackerels. The first of these studies by Soko Gushiken was based on morphological characteristics and found the species was part of a monophyletic clade of the scads and horse mackerels with Atule, Selar, Trachurus and Decapterus, being most closely related to Atule. A 1987 analysis of genetic divergence amongst the scads and horse mackerels using isozyme electrophoresis indicated the species was most closely related to Selar, forming a monophyletic clade with Trachurus, but being more distant from Decapterus. Two studies in 2002 and 2007 of mitochondrial cytochrome b sequences generally agreed that Selaroides was most closely related to Selar (depending on analysis type), however both indicated a closer relationship to the deeper bodied genera such as Caranx and Hemicaranx than to the scads of Trachurus and Decapterus. The yellowstripe scad is a small species, attaining a maximum length of 22 cm, but is more common at lengths less than 15 cm. The species has a body shape typical of many scads, with a compressed elongate, oblong body with the dorsal and ventral profiles equally curved. There is a fairly well developed adipose eyelid on the latter half of the eye. The dentition of the yellowstripe scad is one of the diagnostic features of the species, with the upper jaw and mouth being devoid of any teeth while the lower has a single series of fine villiform teeth. The dorsal fin is in two parts; the first having 8 spines and the second 1 spine and 24 to 26 soft rays. The anal fin has 2 detached spines followed by 20 to 23 soft rays. In one recorded case these two spines were not present. The soft dorsal and anal fins both have scaly basal sheaths. The pectoral fin is falcate and doesn't reach the junction of the curved and straight sections of the lateral line. The pectoral girdle has no groove, and is another defining characteristic. The anterior curve in the lateral line is moderate, with the straight section containing 13 to 25 scales and 24 to 29 small scutes. The breast is completely scaled. There are 40 to 46 gill rakers in total and 24 vertebrae. The yellowstripe scad is a metallic blue to blue-green colour above grading to a silvery white below with a characteristic broad yellow stripe extending from the upper margin of the eye to the caudal peduncle. A black opercular spot is prominent and often extends onto the shoulder. The dorsal, anal and caudal fins are pale to dusky yellow, the pelvic fins are white and the pectoral fins hyaline.