The torpedo scad ( Megalaspis cordyla), also known as the hardtail scad, finny scad, finletted mackerel scad or cordyla scad, is a species of moderately large ocean fish classified in the jack and horse mackerel family, Carangidae. The torpedo scad is distributed throughout the tropical Indo-Pacific region, ranging from South Africa in the west to Tonga in the east, extending to Japan in the north and Australia in south. It is a schooling pelagic fish which occupies the surface layers of both inshore and Shore oceanic waters. The torpedo scad is easily identified by both its 'torpedo' shaped body and a series of detached finlets at the rear of both the dorsal fin and . The largest recorded individual was 80 cm long and weighed 4 kilogram, although it is more common at lengths less than 40 cm. It is a species, taking a variety of fish, and by both active and filter feeding. There is a shift in diet as the species grow; however fish is the dominant prey in all size classes. Torpedo scad reach sexual maturity at 22 cm in females and 26.4 cm in males, with spawning occurring between March and July in India, where significant research into larvae growth and morphometrics has been carried out.
The torpedo scad is of major importance to fisheries throughout the Indo-Pacific, including India. Statistics (which exclude India) show the annual catch of the species has risen from 70,000 in 1997 to 107,000 tonnes in 2007. The major users of the species from this data are Indonesia and Malaysia. The torpedo scad is often taken by angling, however it is considered only marginal table fare and is occasionally used as bait.
Taxonomy and phylogeny
The torpedo scad is the only member of the
monotypic genus
Megalaspis, which is one of the thirty genera in the family
Carangidae, which in turn is part of the order
Carangiformes.
The species was first scientifically described by Carl Linnaeus,
The relationship of the species to other carangids was assessed in Soko Gushiken's 1986 paper on the phylogeny of the Carangidae. It was the sole species in one of three distinct within the tribe Carangini.
Description
torpedo scad is a moderately large fish, growing to a maximum recorded length of 80 cm and a weight of 4
kilogram,
however is more common between 30 and 40 cm length.
It is rare at lengths greater than 80 cm.
The species is often considered to have a rather unusual body form, having features superficially similar to
, mackerels and other carangids. The body is elongate and
subcylindrical, becoming highly compressed toward the tail and
caudal fin, with a marked median keel on the
caudal peduncle.
The dorsal and ventral profiles of the fish are nearly evenly , with the two profiles intersecting at the pointed snout.
There are two separate
; the first consisting of 8 moderately high spines and the second of a single spine followed by 18 to 20 soft rays.
The
anal fin consists of two anteriorally detached spines followed by a single spine attached to 16 or 17 soft rays. In both the dorsal and anal fins, the posterior 7-10 rays are detached and form a series of diagnostic finlets.
The
pectoral fin is strongly falcate (scythe shaped), and extends beyond the origin of the second dorsal fin. The
lateral line is strongly arched over a short length anteriorly, with the intersection of the curved and straight sections vertically below the fourth or fifth spine of the first dorsal fin.
The curved section of the lateral line has 21 to 29 scales, while the straight section has 51 to 59 very large
.
The breast is devoid of scales in a triangular patch to about one-third the distance to the pectoral fin base. The eye has a well-developed
adipose eyelid which nearly completely covers the eye. The upper jaw contains small villiform teeth, with some outer teeth moderately enlarged, while the lower jaw has a single row of small teeth. There are 26 to 32
and 24
vertebrae.
The olfactory apparatus and hypothalamo-neurosecretory system of the species has been extensively described in the Indian scientific literature.
The torpedo scad is bluish-grey to green above, changing to a silvery white on its sides and abdomen. The dorsal and anal fins are pale to yellow, becoming dusky at the outer edges. The pectoral and are also pale with dusky upper halves, while the caudal fin is dark, particularly on the leading and trailing edges. A large black spot is present on the operculum.
Distribution and habitat
The torpedo scad is distributed throughout the
tropical and subtropical waters of the
Indian Ocean and west
.
In the west, the range of the species extends from the tip of
South Africa north along the east African coastline to the
Persian Gulf and
Red Sea. Records of the fish are common from most Indian Ocean islands including the
Maldives,
Seychelles and
Madagascar.
The species is found along the
and
coastlines, extending north to
China and
South Korea on the mainland. It is abundant through the central Indo-Pacific and the Indonesian Archipelago,
with its offshore range extending to
Taiwan and
Japan in the north.
Around
Australia, torpedo scad have been recorded as far south as Fremantle on the west coast and
Sydney on the east coast.
The range of the species extends to several eastern Pacific islands including
Samoa,
New Caledonia and
Tonga.
The torpedo scad is a pelagic schooling species which is found in both far offshore environments as well as more protected inshore environments.
Biology and ecology
torpedo scad is an important species to commercial
fisheries in parts of Asia, and as such has had significant research published on its biology and
ecology. All of this information is published in relatively obscure Indian journals and is unavailable to most institutions. The torpedo scad is a
fish which both consumes larger prey and
filter feeding to consume
organisms.
Larger prey items include a variety of fish and
including
squid and
cuttlefish.
Smaller foods are mostly
such as
,
,
,
and
.
and
are also reported to be minor constituents of the diet of the species.
The species also appears to have dietary shifts as it grows, however in all size classes fish are the dominant prey.
Species recorded as being predators of torpedo scad include species of
Sciaenidae and
requiem shark.
Each sex of the torpedo scad reach
sexual maturity at different lengths; females are mature by 22 cm and males by 26.4 cm.
Other studies have suggested similar lengths, including 17 cm in males and 27 cm in females,
as well as an average of 25 cm in both sexes.
Spawning has not been directly observed, however peaks in
larvae abundance are known from March to July, with a peak in June in India.
the eggs are pelagic, and are spherical and transparent with a
yolk and single oil globule. The larval stage is extensively described, with the species having 24
.
The growth of the species is not reported, however numerous morphometric (length vs weight) studies have been carried out on the species.
The population structure in Indian waters has also been well studied, with the most recent of these suggesting a major recruitment event occurs between May and August. These studies also guide fisheries regulations, with a theoretical maximum yield achieved when fish are only taken once they reach 18 cm.
Relationship to humans
The torpedo scad is of major importance to commercial
fisheries in the central Indo-Pacific region (including India), and of moderate to minor importance elsewhere. Statistics recorded by the
FAO do not include India, however even without this country the annual take of torpedo scad has increased from 70,000 tonnes in 1997 to 107,000 tonnes in 2007.
On the basis of these statistics, the biggest utiliser of the species is Indonesia, with a take of 42,000 tonnes followed by
Malaysia with a take of 22,000 tonnes.
Thailand and the
Philippines also take large quantities of the fish, with around 18,000 tonnes each annually.
countries also record this species in their hauls, but at lower amounts of between 50 and 5000 t.
In more southerly regions such as South Africa, it is a rare catch, usually appearing in beach
seine net.
The species is taken by a variety of netting methods such as beach seines,
, purse seines and other types of trap including hook and line. It is usually marketed fresh, dried or salted.
Torpedo scad are often caught by
angling throughout their range, however are not considered a target for gamefishing. They readily take small lures and are good sport on light tackle.
Torpedo scad are said to have fair to good quality flesh, however are not very popular. Some chefs recommend frying or steaming the fish, although grilling is also acceptable.
In polluted waters it has been demonstrated the fish contain higher than acceptable levels of
heavy metals, and should be avoided in such regions.
Torpedo scad are often used as live baits for larger gamefish.
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