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.
A trio of yellowstripe scad displaying their prominent yellow band
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.
Distribution and habitat
The yellowstripe scad is distributed throughout the tropical and subtropical waters of the Indian and western Pacific Oceans. In the Indian Ocean its ranges from the Persian Gulf and the northern Arabian Peninsula, eastward to India and South East Asia, and down to northern Australia where it is known from Shark Bay in the west to Brisbane in the east. The species is also known from offshore islands such as the Maldives in the Indian Ocean. The yellowstripe scad inhabits the western Pacific Ocean from Japan in the north south to the Indonesian Archipelago and several east Pacific Islands including New Caledonia and Vanuatu.
The yellowstripe scad is predominantly an inshore species, and occurs in large demersal schools over soft substrates. In Australia it inhabits inshore and shallow shelf waters to depths of 50m, while in Malaysia has been recorded to 70 m depth, although is most common between 40 and 60 m depth.
Biology and ecology
The yellowstripe scad is a common schooling species throughout its range, and due to its importance to fisheries has been well studied. In northern Australia, the Philippines and parts of India it has been found to be one of the most common species in these waters. Schools of yellowstripe scad is known to seasonally migrate to coastal waters in summer and back to deeper shelf waters in Taiwan, with no other clear movements recorded throughout its range.
The yellowstripe scad is a predatory fish, taking a variety of crustaceans and other small prey items, with its exact diet varying both spatially and temporally. In northern Australia the most common prey items are ostracods, gastropods and euphausiids. The diet of individuals in India is more varied, with crustaceans, notably decapods and copepods making up the main part of the diet. Small fishes of the genus Anchoviella, pteropods, algal material, diatoms, molluscan larvae and foramanifera make up a lesser part of the diet here also. The species shows some diet partitioning between size classes, and during the year, the diet shifts as prey items vary in abundance. The species is diurnally active in India, while elsewhere in its range, nocturnal feeding has been reported. Unlike some of its relatives, feeding continues during spawning, with no apparent change in food preferences.
The published length that yellowstripe scad become sexually mature at varies between 8.8 cm when less than a year old and 11.4 cm. In his research, Tandon noted that his estimate was much lower than previous studies had suggested, which he explained as sampling bias due to larger net mesh size in the previous work. There is a prolonged breeding season in India, with each individual spawning only once a year. The season extends from July to March with two peaks in January to April and July to October. In morphometric studies conducted in the same area, it was found some morphometric and meristic characters had a variation that was difficult to reconcile as being due to different generations or populations. Instead it was suggested that due to the two major periods of spawning occurring in different seasons.