The
torpedo scad,
Megalaspis cordyla
(also known as the
hardtail scad,
finny
scad,
finletted mackerel scad and
cordyla scad), is a species of moderately large
marine 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
offshore oceanic waters. The torpedo scad is easily
identified by both its 'torpedo' shaped body and a series of
detached
finlet at the
rear of both the
dorsal and
anal fins. The largest recorded individual was 80
cm long and weighed 4
kg, although it is more common at lengths less than
40 cm. It is a
predatory species,
taking a variety of fish,
cephalopods and
crustaceans 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
. Significant research into
larval growth and
morphometrics has been carried out in India.
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
t in 1997 to 107 000 t in 2007.
The major users of the
species from this data are Indonesia
and Malaysia
. The
torpedo scad is often taken by
anglers,
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, a group of
perciform fishes in the suborder
Percoidei.
The species was first
scientifically described by
Carl Linnaeus, a famed Swedish
naturalist who is widely considered the
father of modern
taxonomy. The specimen
described by Linnaeus was erroneously described as being from
"America", and no
holotype is known for the
species. Ronald Frick designated a
neotype
for the species in 1999, however this was rejected as it failed to
satisfy
ICZN regulations. Linnaeus named the
species
Scomber cordyla, placing the fish in the true
mackerel genus, which was a common practice
before the family Carangidae was recognised. The
specific epithet is Latin for "mackerel" or
"young tunny (tuna)". A second independent renaming of the species
occurred in 1793 by
Marcus Elieser
Bloch, who assigned the name
Scomber rottleri, with
several later redescriptions and namings occurring up until 1874.
In 1851
Pieter Bleeker reassigned
Scomber rottleri to its own genus
Megalaspis,
meaning "large
scutes". When
S.
rottleri was found to be a
junior
synonym of
S. cordyla, the name of the species was
finally transferred to
Megalaspis cordyla where it has
remained.
M. cordyla has a variety of
common names, the most common of which is
'torpedo scad', with 'hardtail scad', 'finny scad', 'finletted
mackerel scad' and 'cordyla scad' occasionally used. Because of the
wide range of the species, it has a large collection of non-English
common names also.
The relationship of the species to other carangids was assessed in
Soko Gushiken's 1986 paper on the
phylogeny of the Carangidae. It was one of three
distinct groups within the
subfamily
Caranginae, and formed a
monophyletic
clade with only itself present. The torpedo scad has not been
included in any later genetic phylogenetic studies of the
Carangidae.
Description
The torpedo scad is a moderately large fish, growing to a maximum
recorded length of 80
cm and a weight of
4
kg, however is more common between 30 to
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
tunas,
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
convex, with the two profiles intersecting at
the pointed snout. There are two separate
dorsal fins; 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
finlet. 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
scale, while the straight
section has 51 to 59 very large
scutes. 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
gill
rakers and 24
vertebrae.
The
olfactory apparatus and
hypothalamo-neurosecretory system of the species has been
extensively described in the Indian scientific literature. Also of
note is a report of a heavily deformed individual from India, which
survived past maturity.
The torpedo scad is bluish-grey to green above, changing to a
silvery white on its sides and
belly. The
dorsal and anal fins are pale to yellow, becoming dusky at the
outer edges. The pectoral and
pelvic fins
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
and west Pacific Oceans
. 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 Indian and Asian 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
oceanic environments as
well as more protected
inshore environments.
The fish commonly are found in the upper water column near the
surface waters. It is not found in
estuaries and appears to be intolerant of dirty or
turbid waters. The range of the species extends to more southern
waters in summer as the warm waters push further down the
coasts.
Biology and ecology
The 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
predatory fish which both consumes larger prey and
filter feed to consume
planktonic organisms. Larger prey items include a
variety of fish and
cephalopods including
squid and
cuttlefish. Smaller foods are mostly
crustaceans such as
shrimps,
prawns,
stomatopods,
cladocerans and
crabs.
Molluscs and
gastropods 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
drums 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
larval 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
myomeres. 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
t in 1997 to
107 000 t in 2007.
On the basis of these statistics, the
biggest utiliser of the species is Indonesia, with a take of 42 000
t followed by Malaysia with a take of 22 000 t. Thailand
and the Phillipines
also take large quantities of the fish, with around
18 000 t each annually. Middle
Eastern 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. The species is taken by a
variety of netting methods such as beach seines,
trawls, 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
recreational fishermen 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.
References
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