African threadfish
Encyclopedia
The African threadfish, Alectis alexandrinus, (also known as the Alexandria pompano) is a large species
of marine
fish
in the jack family, Carangidae
. The species is distributed along the coast of tropical Africa
in the eastern Atlantic Ocean
, extending to the Mediterranean Sea
. Adults live predominantly in shallow waters shallower than 70 m deep, often forming small schools. The African threadfish is similar in appearance to the closely related Indian threadfish
, with fin ray counts the most definitive feature of the species. Like other members of the genus Alectis
, the juveniles of the species have long trailing dorsal and anal fin
s. The African threadfish is of minor commercial importance
, and is also considered to be a game fish
.
Alectis
, which itself is one of 33 genera encapsulated in the jack family
Carangidae
. The Carangidae are perciform fishes in the suborder Percoidei
.
The species has a rather confused taxonomic history
, which is based on only two scientific descriptions. The first description was made by the French
naturalist
Étienne Geoffroy Saint-Hilaire
in 1817, in which he named the species Gallus alexandrinus, using the name Gallus after Lacépède recognised the genus separate from Zeus. However, Gallus was preoccupied by a bird, leading to the reassignment of the species to at least six different genera, before the species was correctly placed in Alectis. The second description was made by Georges Cuvier
in 1833 under the name of Gallichthys aegyptiacus. This 'species' was also re evaluated twice, before the description was discarded as a junior synonym of A. alexandrinus. The species has also been incorrectly referred to as Alectis alexandrina as a misspelling of the correct binomial name.
The common names 'African threadfish' and 'Alexandria pompano' are in reference to the species prominent distribution around Africa, as well as the thread like appearance of the juvenile
s dorsal and anal fins.
structure of a large jack, with a distinctly angular, strongly compressed body. The major identifying feature of the species is its head profile, having a slight concavity near the eye
s which distinguishes it from the African pompano
. The dorsal profile of the fish is more curved than the ventral profile, and the body is deepest between the origins of the soft dorsal
and soft anal fins. The first section of the dorsal fin consists of 5 to 7 visible spines, with the second section having one spine and 20 to 22 soft rays. The anal fin has two spines followed by a single spine and 18 or 19 soft rays. The pectoral fin is long and curved, extending beyond the junction of the straight and curved sections of the lateral line
. Anterior to the caudal fin are two oblate keels on each side of the line of scutes. The body appears to be scaleless, but on closer inspection has minute, deeply embedded scales
. The lateral line is strongly curved anteriorly, with a section of 6 to 11 scute
s toward the tail. Juveniles and often adults have long, filamentous trailing first anal and dorsal fin spine. The species grows to at least 1 m in length.
The fish is a silver colour, often with blue and greenish tints and reflection, especially when fresh. The fins are all a pale silvery green to blue colour, or hyaline
. Juveniles may show two dark bands on their lower bodies.
, inhabiting the waters of West Africa
from Morocco
around to Angola
. The species also has had several individuals taken from the Mediterranean and one extreme capture in the Adriatic Sea
s.
Adults are generally solitary in coastal waters, occupying lower parts of the water column, down to at least 70 m. Juveniles are usually pelagic and drift with ocean currents, sometimes ending up in estuarine environments.
, with only the diet
of the species confirmed. The African threadfish feeds on squid
and other fishes. The reproduction in the species is largely unknown, but observations on Alectis ciliaris suggest individual fish may pair and then spawn
.
, especially in larger sizes. The species is rarely targeted by anglers though, due to its comparative rarity. The fish also fetches high prices at market
, unlike many other members of the Carangidae.
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 marine
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 distributed along the coast of tropical Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
in the eastern Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, extending to 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...
. Adults live predominantly in shallow waters shallower than 70 m deep, often forming small schools. The African threadfish is similar in appearance to the closely related Indian threadfish
Indian threadfish
The Indian threadfish, Alectis indicus, is a large species of coastal marine fish of the jack family, Carangidae. The species is widespread in the waters of the tropical Indo-West Pacific Ocean, ranging from east Africa to India, Asia, Indonesia and Australia...
, with fin ray counts the most definitive feature of the species. Like other members of the genus Alectis
Alectis
Alectis is a genus of fish in the family Carangidae containing three extant species, all of which are large marine fishes. They are commonly known as threadfish, diamond trevallies and occasionally pompanos, although they have no close affiliation with the true pompano genus.-Taxonomy:Alectis is...
, the juveniles of the species have long trailing dorsal and anal fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
s. The African threadfish is of minor commercial 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,...
, and is also considered to be a game fish
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
.
Taxonomy
The African threadfish is one of three members of the diamond trevally 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...
Alectis
Alectis
Alectis is a genus of fish in the family Carangidae containing three extant species, all of which are large marine fishes. They are commonly known as threadfish, diamond trevallies and occasionally pompanos, although they have no close affiliation with the true pompano genus.-Taxonomy:Alectis is...
, which itself is one of 33 genera encapsulated in the jack family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
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
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 species has a rather confused 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...
, which is based on only two scientific descriptions. The first description was made by the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Étienne Geoffroy Saint-Hilaire
Étienne Geoffroy Saint-Hilaire
Étienne Geoffroy Saint-Hilaire was a French naturalist who established the principle of "unity of composition". He was a colleague of Jean-Baptiste Lamarck and expanded and defended Lamarck's evolutionary theories...
in 1817, in which he named the species Gallus alexandrinus, using the name Gallus after Lacépède recognised the genus separate from Zeus. However, Gallus was preoccupied by a bird, leading to the reassignment of the species to at least six different genera, before the species was correctly placed in Alectis. The second description was made by Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
in 1833 under the name of Gallichthys aegyptiacus. This 'species' was also re evaluated twice, before the description was discarded as a junior synonym of A. alexandrinus. The species has also been incorrectly referred to as Alectis alexandrina as a misspelling of the correct binomial name.
The common names 'African threadfish' and 'Alexandria pompano' are in reference to the species prominent distribution around Africa, as well as the thread like appearance of the juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
s dorsal and anal fins.
Description
The African threadfish has the typical bodyBody
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
structure of a large jack, with a distinctly angular, strongly compressed body. The major identifying feature of the species is its head profile, having a slight concavity near the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s which distinguishes it from the African pompano
African pompano
The African pompano, Alectis ciliaris, is a widely distributed species of tropical marine fish in the Jack family, Carangidae. The species is found in tropical waters worldwide, with adults often inhabiting coastlines while juveniles are usually pelagic, floating with ocean currents...
. The dorsal profile of the fish is more curved than the ventral profile, and the body is deepest between the origins of the soft dorsal
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...
and soft anal fins. The first section of the dorsal fin consists of 5 to 7 visible spines, with the second section having one spine and 20 to 22 soft rays. The anal fin has two spines followed by a single spine and 18 or 19 soft rays. The pectoral fin is long and curved, extending beyond the junction of the straight and curved sections 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...
. Anterior to the caudal fin are two oblate keels on each side of the line of scutes. The body appears to be scaleless, but on closer inspection has minute, deeply embedded scales
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...
. The lateral line is strongly curved anteriorly, with a section of 6 to 11 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 toward the tail. Juveniles and often adults have long, filamentous trailing first anal and dorsal fin spine. The species grows to at least 1 m in length.
The fish is a silver colour, often with blue and greenish tints and reflection, especially when fresh. The fins are all a pale silvery green to blue colour, or 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...
. Juveniles may show two dark bands on their lower bodies.
Distribution and habitat
The African threadfish is primarily distributed throughout the tropical eastern Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, inhabiting the waters of West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
from Morocco
Morocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
around to Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
. The species also has had several individuals taken from the Mediterranean and one extreme capture in the Adriatic Sea
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...
s.
Adults are generally solitary in coastal waters, occupying lower parts of the water column, down to at least 70 m. Juveniles are usually pelagic and drift with ocean currents, sometimes ending up in estuarine environments.
Biology
Limited information is available on the species biologyBiology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, with only the diet
Diet (nutrition)
In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...
of the species confirmed. The African threadfish feeds on squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and other fishes. The reproduction in the species is largely unknown, but observations on Alectis ciliaris suggest individual fish may pair and then 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...
.
Relationship to humans
The species is of minor importance to local fisheries throughout its range, and is also considered a good game fishGame fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
, especially in larger sizes. The species is rarely targeted by anglers though, due to its comparative rarity. The fish also fetches high prices at market
Market
A market is one of many varieties of systems, institutions, procedures, social relations and infrastructures whereby parties engage in exchange. While parties may exchange goods and services by barter, most markets rely on sellers offering their goods or services in exchange for money from buyers...
, unlike many other members of the Carangidae.