The herring scad (Alepes vari), also referred to as the duskyfin crevalle and trevally scad, represents a prevalent species of tropical marine fish within the family Carangidae. This species predominantly inhabits the surface waters of coastal regions across the Indo-West Pacific, preying on an array of crustaceans and small fish. Distinguished as the largest fish within the genus Alepes, the herring scad can attain lengths of up to 56 cm. Notable identification features include its numerous, smaller scutes and the specific count of gill rakers on its first arch. Despite its widespread distribution, the species holds minor significance to fisheries.
Comprising part of the scad genus Alepes, the herring scad is one of five extant species within this group, all of which belong to the broader jack family, Carangidae, under the order Carangiformes.
In terms of morphology, the herring scad exhibits a body profile akin to other members of Alepes, characterized by a strongly compressed, ovate form. Its dorsal and ventral profiles are nearly uniformly convex, culminating in a pointed snout at the anterior. The species features two distinct dorsal fins: the first comprises eight spines, while the second contains a single spine followed by 24 to 27 soft rays. The anal fin has two anteriorly detached small spines and a single spine linked to 20 to 23 soft rays. The lateral line displays a pronounced anterior arch, with the curved and straight sections meeting between the origin of the second dorsal and third soft ray. This curved section includes 42 to 50 scales and 0 to 2 scutes, whereas the straight counterpart consists of 0 to 7 scales and 48 to 69 scutes. Additionally, the species has a well-developed adipose eyelid on the posterior eye segment. The jaws house a single row of numerous comb-like teeth, complemented by 32 to 38 gill rakers and a total of 24 vertebrae. While the species can grow as large as 56 cm, more common sightings are of individuals below 30 cm.
In appearance, the herring scad's upper body manifests as ash blue, transitioning to a silvery white underside, punctuated by a diffuse dusky blotch on the operculum margin. The fins generally have a dusky hue, except for the spinous dorsal fin, which varies from pale to dark dusky. Sexual dimorphism is evident in the fin pigmentation, with males developing darker spinous dorsal fins and lobes of the soft dorsal, anal, and pelvic fins compared to females.
Geographically, the herring scad spans tropical to subtropical regions of the Indo-West 🌊 Pacific Oceans. Its distribution ranges from the 🌊 Red Sea, extending eastwards to encompass 🇱🇰 Sri Lanka, 🇮🇳 India, Southeast Asia, 🇨🇳 China, 🇮🇩 Indonesia, the 🇵🇭 Philippines, 🇵🇬 New Guinea, reaching as far north as 🇹🇼 Taiwan and as far south as northern 🇦🇺 Australia. The species predominantly resides in shallow coastal areas, occupying the surface layers above diverse substrates.
In its carnivorous diet, the herring scad primarily consumes crustaceans such as shrimp, copepods, and decapods, alongside other small fish. Notably, it is one of several pelagic fish species from the 🌊 Red Sea hosting a high concentration of luminescent bacteria within its gut, which coexist symbiotically as part of their gut flora.
Parasites affecting the herring scad include the philometrid nematode Philometra austropacifica, which resides within the ovaries of female fish.
Economically, the species holds limited commercial value, occasionally captured using hook and line fishing methods.
Why it's threatened
Threat classification from the IUCN Red List.
