Shrimp scad
Encyclopedia
The shrimp scad, Alepes djedaba (also known as the slender yellowtail kingfish), is a species
of widespread tropical marine
fish
of the jack family, Carangidae
. The shrimp scad is widely distributed in the tropical and subtropical western Indian Ocean
and areas of the eastern Pacific Ocean
, ranging from South Africa
in the west to Hawaii
in the east, including Japan and Australia to the north and south. The species is commonly found on inshore reef
s and sandy substrates. It has the common body profile of a scad, and may be difficult to differentiate from others in the genus Alepes
. It is one of the larger scads, growing to 40 cm, but often is encountered at much smaller sizes. The shrimp scad often forms large schools, and is carnivorous, consuming a variety of crustacean
s and small fish. It is of moderate importance to fisheries throughout its range.
Alepes, which itself is one of thirty genera in the jack family Carangidae
. The Carangidae are Perciform fishes in the suborder Percoidei.
A molecular phylogenetic study has confirmed the genus Alepes is supported, at least between A. djedaba and A. kleinii which are closely related.
The shrimp scad was first scientifically described by Swedish naturalist Peter Forsskål
from a specimen collected in the Red Sea in 1775, which was designated to be the holotype. He named the species Scomber djedaba, placing it in the mackerel
genus, a common practice with carangids at the time, as the family Carangidae was yet to be erected. A number of taxonomists have since tried to reclassify the species in a more parsimonious genus, with a number of carangid genera proposed including Selar, Caranx
and Atule. To add to the confusion over the species, the species was redescribed twice after the first naming, once by Cuvier
who named it Caranx kalla, and once by Fowler
who proposed Caranx microbrachium for the species. Caranx kalla was subsequently placed in the genus Atule, but is now considered, along with Caranx microbrachium to be a junior synonym, unacceptable under the ICZN
rules and has been discarded. The currently accepted name of Alepes djedaba was proposed by Gushiken in an extensive review of the carangidae of Japan, identifying a number of morphological features associating it with Alepes. Due to the awkward species name, the species is often misspelt as djeddaba in the literature.
, compressed body and dorsal and ventral profiles which are almost evenly convex. The snout
is pointed and the eye diameter is nearly equal to the snout length, with an adipose eyelid well developed on the posterior half of eye. There are two moderately high, separate dorsal fin
s, the first of which has eight spines, while the second has a single spine followed by 23 to 25 soft rays. The anal fin has two detached spines followed by one spine connected to 18 to 20 soft rays. The anterior section of the lateral line
is strongly curved, containing thirty one to thirty six scale
s, while the straight section consists of seventy seven to eighty five scute
s.
The colour of the body is an overall silver colour, with a green-blue tone on the upper body, while the underside fades to a more white colour. There is a diffuse dusky blotch on margin of operculum
which is bordered by a smaller white spot. The spinous dorsal fin, including
the last dorsal fin spine is blackish or dusky, the soft dorsal fin is blackish or dusky above the scaly sheath and the margin of first to fourth upper soft rays is whitish. The middle portion of the anal fin below the scaly sheath is slightly blackish or dusk. The caudal fin is often a striking yellow, especially when fresh, with the upper caudal lobe often fading to a darker shade. The posterior scutes may also be a yellow to rusty colour, especially after removal from the water.
region from South Africa
in the west, along the coasts of East Africa
, India
, Asia
, Indonesia
, northern Australia
, Japan
and extending as far east as Hawaii
. They are also one of the species involved in the Lessepsian migration through the Suez Canal
and inhabit the east coast of the Mediterranean Sea
around Israel, Lebanon and Egypt.
The species is primarily an inshore inhabitant of reef
s and over open sand patches, even in moderately turbid waters, often forming large schools. The species has in isolated circumstances also been found close to shore in surf zones in Japan and in estuarine waters in South Africa. The species is occasionally found in offshore environments, suggesting it can lead a pelagic lifestyle also.
species, with records from India indicating the fish resides and feeds in the waters of Madras from September to May, before migrating elsewhere to spawn
. The shrimp scad feeds on a variety of prey, with at least two shifts in diet occurring as the fish mature. Older individuals feed mainly on young fishes, crustaceans like decapods, ostracod
s, amphipods and cladocerans with minor amounts of nematodes, insect body parts and insect larvae taken. Fish within a length range of 150–199 mm and 240–319 mm showed a preference for young fishes, while those in the length range of 200–239 mm primarily consumed ostracods and other crustaceans. Based on the food items taken, the species is an active midwater feeder. There is less food consumed during breeding season, which is indicative of reduced feeding activity during that period. Sexual maturity
is attained by about 17 cm fork length and spawning is thought to occur in shallow coastal waters.
The species is of moderate commercial interest
in most countries where it is often considered too small to be worthwhile and is often caught on hook and line tackle and in seines as bycatch. It is often taken by subsistence fisheries using various traditional gear such as inter-tidal fixed stake traps. Around the Asian and Indonesian coasts, larger numbers are taken than anywhere else in its range and it is considered a good eating fish.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of widespread tropical marine
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
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...
of 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 shrimp scad is widely distributed in the tropical and subtropical western Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and areas of the eastern Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, ranging from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in the west to Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
in the east, including Japan and Australia to the north and south. The species is commonly found on inshore reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s and sandy substrates. It has the common body profile of a scad, and may be difficult to differentiate from others 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...
. It is one of the larger scads, growing to 40 cm, but often is encountered at much smaller sizes. The shrimp scad often forms large schools, and is carnivorous, consuming a variety of 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 small fish. It is of moderate importance to fisheries throughout its range.
Taxonomy and naming
The shrimp scad is one of five species of fish in the scad genusGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Alepes, which itself is one of thirty genera 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 Carangidae are Perciform fishes in the suborder Percoidei.
A molecular phylogenetic study has confirmed the genus Alepes is supported, at least between A. djedaba and A. kleinii which are closely related.
The shrimp scad was first scientifically described by Swedish naturalist Peter Forsskål
Peter Forsskål
Peter Forsskål, sometimes spelled Pehr Forsskål, Peter Forskaol, Petrus Forskål or Pehr Forsskåhl, was a Swedish explorer, orientalist, naturalist and an apostle of Carl Linnaeus.-Early life:...
from a specimen collected in the Red Sea in 1775, which was designated to be the holotype. He named the species Scomber djedaba, placing it in the mackerel
Scombridae
Scombridae is the family of the mackerels, tunas, and bonitos, and thus includes many of the most important and familiar food fishes. The family consists of about 55 species in 15 genera and two subfamilies...
genus, a common practice with carangids at the time, as the family Carangidae was yet to be erected. A number of taxonomists have since tried to reclassify the species in a more parsimonious genus, with a number of carangid genera proposed including Selar, Caranx
Caranx
Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...
and Atule. To add to the confusion over the species, the species was redescribed twice after the first naming, once by Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
who named it Caranx kalla, and once by Fowler
Henry Weed Fowler
Henry Weed Fowler was an American zoologist born in Holmesburg, Pennsylvania.He studied at Stanford University under David Starr Jordan...
who proposed Caranx microbrachium for the species. Caranx kalla was subsequently placed in the genus Atule, but is now considered, along with Caranx microbrachium to be a junior synonym, unacceptable 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 and has been discarded. The currently accepted name of Alepes djedaba was proposed by Gushiken in an extensive review of the carangidae of Japan, identifying a number of morphological features associating it with Alepes. Due to the awkward species name, the species is often misspelt as djeddaba in the literature.
Description
The shrimp scad is can grow to a large size compared to other scads, reaching a maximum known length of 40 cm, but more often seen around 25 cm. The shrimp scad has a body profile very similar to other scads and some other carangids, with an oblongRectangle
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...
, compressed body and dorsal and ventral profiles which are almost evenly convex. The snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...
is pointed and the eye diameter is nearly equal to the snout length, with an adipose eyelid well developed on the posterior half of eye. There are two moderately high, separate dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
s, the first of which has eight spines, while the second has a single spine followed by 23 to 25 soft rays. The anal fin has two detached spines followed by one spine connected to 18 to 20 soft rays. The anterior section of the lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
is strongly curved, containing thirty one to thirty six scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s, while the straight section consists of seventy seven to eighty five 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.
The colour of the body is an overall silver colour, with a green-blue tone on the upper body, while the underside fades to a more white colour. There is a diffuse dusky blotch on margin of 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....
which is bordered by a smaller white spot. The spinous dorsal fin, including
the last dorsal fin spine is blackish or dusky, the soft dorsal fin is blackish or dusky above the scaly sheath and the margin of first to fourth upper soft rays is whitish. The middle portion of the anal fin below the scaly sheath is slightly blackish or dusk. The caudal fin is often a striking yellow, especially when fresh, with the upper caudal lobe often fading to a darker shade. The posterior scutes may also be a yellow to rusty colour, especially after removal from the water.
Distribution and habitat
The shrimp scad is distributed throughout the Indo-PacificIndo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
region from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
in the west, along the coasts of East Africa
East Africa
East Africa or Eastern Africa is the easterly region of the African continent, variably defined by geography or geopolitics. In the UN scheme of geographic regions, 19 territories constitute Eastern Africa:...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, 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...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and extending as far east as Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. They are also one of the species involved in the Lessepsian migration through the Suez Canal
Suez Canal
The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...
and inhabit the east coast of the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
around Israel, Lebanon and Egypt.
The species is primarily an inshore inhabitant of reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s and over open sand patches, even in moderately turbid waters, often forming large schools. The species has in isolated circumstances also been found close to shore in surf zones in Japan and in estuarine waters in South Africa. The species is occasionally found in offshore environments, suggesting it can lead a pelagic lifestyle also.
Biology and fishery
The shrimp scad is known to be a migratoryFish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
species, with records from India indicating the fish resides and feeds in the waters of Madras from September to May, before migrating elsewhere to spawn
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
. The shrimp scad feeds on a variety of prey, with at least two shifts in diet occurring as the fish mature. Older individuals feed mainly on young fishes, crustaceans like decapods, ostracod
Ostracod
Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
s, amphipods and cladocerans with minor amounts of nematodes, insect body parts and insect larvae taken. Fish within a length range of 150–199 mm and 240–319 mm showed a preference for young fishes, while those in the length range of 200–239 mm primarily consumed ostracods and other crustaceans. Based on the food items taken, the species is an active midwater feeder. There is less food consumed during breeding season, which is indicative of reduced feeding activity during that period. Sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
is attained by about 17 cm fork length and spawning is thought to occur in shallow coastal waters.
The species is of moderate commercial interest
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,...
in most countries where it is often considered too small to be worthwhile and is often caught on hook and line tackle and in seines as bycatch. It is often taken by subsistence fisheries using various traditional gear such as inter-tidal fixed stake traps. Around the Asian and Indonesian coasts, larger numbers are taken than anywhere else in its range and it is considered a good eating fish.