Smallmouth scad
Encyclopedia
The smallmouth scad, Alepes apercna (also known as the banded scad and roundfin trevally), is a species of tropical marine
fish
in the jack family Carangidae
. The species is endemic to northern Australia
, inhabiting primarily inshore waters. It is similar to other scads in the genus Alepes
, and is distinguished by a well-developed posterior adipose eyelid, as well as fin membrane spotting and gill raker counts. It is not a large species, with the maximum length reported to be 29.5 cm. It feeds primarily on a variety of small invertebrate
s, and is of very minor economic importance
.
. The Carangidae are perciform fish in the suborder Percoidei
.
The smallmouth scad has a slightly confusing taxonomic history
, with confusion over the classification, the author, and confusion with other species clouding the species past. The first specimen known to science
was taken in 1984, and deposited in the Queensland Museum
along with photographs of a juvenile as paratype
s with no holotype
designated. Grant described the species for the first time in 1987 in "Fishes of Australia", crediting the species to Smith-Vaniz, who presumably collected the specimen and wrote a brief description. However, Grant's description of the species is the first publication of the species, making him the correct author under the ICZN
rules. Confusion over this species and Alepes kleinii led Sainsbury to refer to the species as Alepes sp., with the placement in the genus considered somewhat dubious. The type locality is listed only as Australia.
The common name
of the species is related to the small mouth size of the species, with the names banded scad and roundfin trevally used incorrectly, and this is partially due to confusion with A. kleinii, the true banded scad.
to oblong
shaped body which is strongly compressed. The snout is blunt, and both the ventral and dorsal profiles are equally convex. The dorsal and anal fins both have a low profile, and are not falcate, while the pectorals are falcate and extend beyond the junction of the curved and straight lateral line. The curved section of the lateral line is strongly arched, rising from the origin at the operculum
and terminating at the junction with the straight section. A posterior adipose eyelid is well developed and reaches almost to the center of the eye, and the jaws are filled with fine teeth. The first dorsal fin has 8 spines, and the second dorsal has one spine and 24-26 soft rays. The anal fin has two separate spines posterior to the main anal fin which consists of one spine and 20 to 22 soft rays. There are 51-70 moderately protrusive scute
s. It is similar to Atule mate, but lacks the adipose eyelid on both posterior and anterior sides of the orbit. It is also very similar to Alepes melanoptera and is distinguished from it by having dusky to hyaline dorsal intermembranes, compared to A. melanoptera's spotted membranes. Alepes vari is more similar still, and can be clearly distinguished by gill raker
counts, having 27-30 compared to A. vari's 37. The largest specimen known was taken by the CSIRO and measured 29.5 cm.
The colour of the body is a blue to green blue above and silver below, with young specimens having dark vertical cross bars. The operculum has a diffuse dark blotch .The spinous and soft dorsal fins, anal fins and caudal fin are a dusky yellow green. The anterior of the soft dorsal and anal fins have white tips and the pelvic fin is a white to grey colour, while the pectoral is hyaline
.
n waters, inhabiting the tropical north from Exmouth Gulf
in Western Australia
, north to the Northern Territory
and east to Wide Bay in Queensland
. There has been a single report of an individual as far down as Botany Bay
in New South Wales
. The species may also occur in the Gulf of Papua
but has not yet reported. It is an abundant fish on the continental shelf
in waters from 10 to 150 m in depth, rarely leading a pelagic lifestyle.
s, primarily benthic crustacean
s and molluscs. It also frequently ingests algae
, a feature which is rare in the Carangidae. Nothing of the reproductive cycle is known. It is of little importance to fisheries, usually caught on hook and line tackle by commercial and recreational
fishermen.
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
in the jack family Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
. The species is endemic to northern Australia
Northern Australia
The term northern Australia is generally known to include two State and Territories, being Queensland and the Northern Territory . The part of Western Australia north of latitude 26° south—a definition widely used in law and State government policy—is also usually included...
, inhabiting primarily inshore waters. It is similar to other scads in the genus Alepes
Alepes
Alepes is a genus containing five extant species of tropical marine fishes in the jack family, Carangidae. They are commonly known as scads, a term applied to many genera of carangid fishes. Their body form, however, differs from these other scads by being much more ovate in shape, more similar to...
, and is distinguished by a well-developed posterior adipose eyelid, as well as fin membrane spotting and gill raker counts. It is not a large species, with the maximum length reported to be 29.5 cm. It feeds primarily on a variety of small invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, and is of very minor economic importance
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
.
Taxonomy and naming
The smallmouth scad is one of five members in the scad genus Alepes, which is one of 33 genera of the jack family, CarangidaeCarangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
. The Carangidae are perciform fish in the suborder Percoidei
Percoidei
Percoidei is one of eighteen suborders of bony fish in the order Perciformes. Many commercially harvested fish species are contained in this suborder, including the snappers, jacks, whitings, groupers, bass, perches and porgies.-Divisions:...
.
The smallmouth scad has a slightly confusing taxonomic history
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
, with confusion over the classification, the author, and confusion with other species clouding the species past. The first specimen known to science
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
was taken in 1984, and deposited in the Queensland Museum
Queensland Museum
The Queensland Museum is the state museum of Queensland. The museum currently operates four separate campuses; at South Brisbane, Ipswich, Toowoomba and Townsville.The museum is funded by the State Government of Queensland.-History:...
along with photographs of a juvenile as paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
s with no holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
designated. Grant described the species for the first time in 1987 in "Fishes of Australia", crediting the species to Smith-Vaniz, who presumably collected the specimen and wrote a brief description. However, Grant's description of the species is the first publication of the species, making him the correct author under the ICZN
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
rules. Confusion over this species and Alepes kleinii led Sainsbury to refer to the species as Alepes sp., with the placement in the genus considered somewhat dubious. The type locality is listed only as Australia.
The common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
of the species is related to the small mouth size of the species, with the names banded scad and roundfin trevally used incorrectly, and this is partially due to confusion with A. kleinii, the true banded scad.
Description
The smallmouth scad has an elongate ovalOval
An oval is any curve resembling an egg or an ellipse, such as a Cassini oval. The term does not have a precise mathematical definition except in one area oval , but it may also refer to:* A sporting arena of oval shape** a cricket field...
to oblong
Rectangle
In Euclidean plane geometry, a rectangle is any quadrilateral with four right angles. The term "oblong" is occasionally used to refer to a non-square rectangle...
shaped body which is strongly compressed. The snout is blunt, and both the ventral and dorsal profiles are equally convex. The dorsal and anal fins both have a low profile, and are not falcate, while the pectorals are falcate and extend beyond the junction of the curved and straight lateral line. The curved section of the lateral line is strongly arched, rising from the origin at the operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
and terminating at the junction with the straight section. A posterior adipose eyelid is well developed and reaches almost to the center of the eye, and the jaws are filled with fine teeth. The first dorsal fin has 8 spines, and the second dorsal has one spine and 24-26 soft rays. The anal fin has two separate spines posterior to the main anal fin which consists of one spine and 20 to 22 soft rays. There are 51-70 moderately protrusive scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s. It is similar to Atule mate, but lacks the adipose eyelid on both posterior and anterior sides of the orbit. It is also very similar to Alepes melanoptera and is distinguished from it by having dusky to hyaline dorsal intermembranes, compared to A. melanoptera's spotted membranes. Alepes vari is more similar still, and can be clearly distinguished by gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
counts, having 27-30 compared to A. vari's 37. The largest specimen known was taken by the CSIRO and measured 29.5 cm.
The colour of the body is a blue to green blue above and silver below, with young specimens having dark vertical cross bars. The operculum has a diffuse dark blotch .The spinous and soft dorsal fins, anal fins and caudal fin are a dusky yellow green. The anterior of the soft dorsal and anal fins have white tips and the pelvic fin is a white to grey colour, while the pectoral is hyaline
Hyaline
The term hyaline denotes a substance with a glass-like appearance.-Histopathology:In histopathological medical usage, a hyaline substance appears glassy and pink after being stained with haematoxylin and eosin — usually it is an acellular, proteinaceous material...
.
Distribution and habitat
The smallmouth scad is known only from AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n waters, inhabiting the tropical north from Exmouth Gulf
Exmouth Gulf
Exmouth Gulf is a gulf in the north west of Western Australia. It lies between North West Cape and the main coastline of Western Australia. It is considered to be part of the region of the North West Shelf and in the Canning Basin area.-Environment:...
in Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, north to the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
and east to Wide Bay in Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
. There has been a single report of an individual as far down as Botany Bay
Botany Bay
Botany Bay is a bay in Sydney, New South Wales, a few kilometres south of the Sydney central business district. The Cooks River and the Georges River are the two major tributaries that flow into the bay...
in New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
. The species may also occur in the Gulf of Papua
Gulf of Papua
The Gulf of Papua is a 400 kilometer wide region on the south shore of New Guinea. Some of New Guinea's largest rivers, such as the Fly River, Turama River, Kikori River and Purari River, flow into the gulf, making it a large delta. While the western coast is characterized by swampy tidal...
but has not yet reported. It is an abundant fish on the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
in waters from 10 to 150 m in depth, rarely leading a pelagic lifestyle.
Biology and fishery
Smallmouth scad are omnivorous, but take a high proportion of small invertebrateInvertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, primarily benthic crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s and molluscs. It also frequently ingests algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, a feature which is rare in the Carangidae. Nothing of the reproductive cycle is known. It is of little importance to fisheries, usually caught on hook and line tackle by commercial and recreational
Angling
Angling is a method of fishing by means of an "angle" . The hook is usually attached to a fishing line and the line is often attached to a fishing rod. Fishing rods are usually fitted with a fishing reel that functions as a mechanism for storing, retrieving and paying out the line. The hook itself...
fishermen.