Atractoscion Aequidens
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The geelbeck croaker (''Atractoscion aequidens''), also known as the African weakfish or Cape salmon, is a species of marine
ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...
belonging to the
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Sciaenidae Sciaenidae is a family (biology), family of ray-finned fishes belonging to the Order (biology), order Acanthuriformes. They are commonly called drums or croakers in reference to the repetitive throbbing or drumming sounds they make. The family co ...
, the drums and croakers. This species is found in the southwestern
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...
off southeastern Africa.


Taxonomy

The geelbeck croaker was first formally described as ''Otolithus aequidens'' in 1830 by the French
zoologist Zoology ( , ) is the scientific study of animals. Its studies include the structure, embryology, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. Zoology is one ...
Georges Cuvier Jean Léopold Nicolas Frédéric, baron Cuvier (23 August 1769 – 13 May 1832), known as Georges Cuvier (; ), was a French natural history, naturalist and zoology, zoologist, sometimes referred to as the "founding father of paleontology". Cuv ...
with its type locality given as
False Bay False Bay (Afrikaans: ''Valsbaai'') is a body of water in the Atlantic Ocean between the mountainous Cape Peninsula and the Hottentots Holland Mountains in the extreme south-west of South Africa. The mouth of the bay faces south and is demarc ...
in the
Western Cape The Western Cape ( ; , ) is a provinces of South Africa, province of South Africa, situated on the south-western coast of the country. It is the List of South African provinces by area, fourth largest of the nine provinces with an area of , an ...
. In 1862
Theodore Gill Theodore Nicholas Gill (March 21, 1837 – September 25, 1914) was an American ichthyologist, mammalogist, malacologist, and librarian. Career Born and educated in New York City under private tutors, Gill early showed interest in natural hist ...
classified ''O. aequidens'' in a new
monospecific genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...
''
Atractoscion ''Atractoscion'' is a genus of marine ray-finned fished belonging to the family Sciaenidae, the drums and croakers. The fishes in this genus are found in the Atlantic, Indian and Pacific Oceans. Taxonomy ''Atractoscion'' was first proposed as a ...
'' and designated it as the
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
of that genus. Previously it was considered that this species had a wide distribution in the southeastern Atlantic and
Indo-West Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the s ...
but in 2017 workers described two new species and resurrected '' A. atelodus'' from the western Pacific, restricting this species to the southwestern Indian Ocean. This species is classified in the family Sciaenidae which is placed within the
suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
Sciaenoidei Sciaenoidei is a suborder of ray-finned fishes belonging to the Order (biology), order Acanthuriformes. Taxonomy The suborder was first proposed in 1828 by the French zoologist Georges Cuvier. The 5th edition of ''Fishes of the World'' classifies ...
of the
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
Acanthuriformes Acanthuriformes is a large, diverse order of mostly marine ray-finned fishes, part of the Percomorpha clade. In the past, members of this clade were placed in the suborders Acanthuroidea and Percoidea of the order Perciformes, but this treatment ...
in the 5th edition of ''
Fishes of the World ''Fishes of the World'' is a standard reference for the systematics of fishes. It was first written in 1976 by the American ichthyologist Joseph S. Nelson (1937–2011). Now in its fifth edition (2016), the work is a comprehensive overview of t ...
''. The
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
''aequidens'' means "equal teeth", alluding to the similar sized teeth and lack of canines.


Description

The geelbeck croaker has 9 spines in the front part of the
dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...
separated from the rear part by an incision and a single spine and 27 or 28 soft rays behind the incision. The
anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...
is supported by 2 spines and 9 or 10 soft rays. There are between 16 and 18 fin rays in the
pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...
. Its body has a
standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...
which is equivalent to 4.5 to 5.2 times its depth. All of the teeth in the mouth can be depressed. The colour of the body is iridescent blue and purple with bright yellow on the edges of jaws and the inside of the operculum. There is a blotch on the
axil A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, fl ...
of the pectoral-fin. This species has a maximum published
total length Fish measurement is the measuring of individual fish and various parts of their anatomies, for data used in many areas of ichthyology, including taxonomy and fishery biology. Overall length Standard length (SL) is the length of a fish measured f ...
of , although is more typical, and a maximum published weight of .


Distribution and habitat

The geelbeck croaker is found in the southwestern Indian Ocean from
Cape Agulhas Cape Agulhas (; , "Cape of Needles") is a rocky headland in Western Cape, South Africa. It is the geographic southern tip of Africa and the beginning of the traditional dividing line between the Atlantic and Indian oceans according to the In ...
east along the South African coast and north as far as Pinda in the
Zambezia Province Zambezia ( ) is the second most-populous province of Mozambique, located in the central coastal region south-west of Nampula Province and north-east of Sofala Province. It has a population of 5.11 million, according to the 2017 census. The provin ...
of Mozambique. The adults gather in
school A school is the educational institution (and, in the case of in-person learning, the Educational architecture, building) designed to provide learning environments for the teaching of students, usually under the direction of teachers. Most co ...
s offshore over sandy bottom, on rocky reefs, and close to wrecks and pinnacles, at depths between > the juveniles are occasionally found in estuaries.


Biology

Geelbeck croakers are nocturnal
piscivore A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted repti ...
s, the adults feed on
pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that live on or near the bottom, and reef fish that are associated with coral reefs. ...
like pilchard ('' Sardinops sagax'')., as well as Japanese anchovy (''Engraulis japonicus''), and
Cape horse mackerel The Cape horse mackerel (''Trachurus capensis'') is a mackerel-like species in the family Carangidae. It is a pelagic species of the south eastern Atlantic Ocean which is a target of fisheries, mainly as bycatch. Description The Cape horse macke ...
(''Trachurus capensis''). These fishes are migratory, the adults undertaking a well defined annual migration along the eastern coast of South Africa. This starts in the Spring when adult fish from the Western Cape to
KwaZulu-Natal KwaZulu-Natal (, also referred to as KZN) is a Provinces of South Africa, province of South Africa that was created in 1994 when the government merged the Zulu people, Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu language, Zulu) and ...
move inshore to
spawn Spawn or spawning may refer to: * Spawning, the eggs and sperm of aquatic animals Arts, entertainment and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** ''Spawn: Armageddon' ...
before moving back off shore during the summer and dispersing over the
Agulhas Bank The Agulhas Bank (, from Portuguese for Cape Agulhas, ''Cabo das Agulhas'', "Cape of Needles") is a broad, shallow part of the southern African continental shelf which extends up to south of Cape Agulhas before falling steeply to the abyssal pla ...
. The pelagic eggs and larvae drift in a southwesterly direction following the inshore peripheral waters of the Agulhas Current. They then spend one or two years in a nursery are in the southeast Cape and then join the sub-adult population off the southern coast of Western Cape, where they remain for a three to four more years. These subadults move inshore in summer and back offshore in winter, until they reach sexual maturity.


Fisheries and conservation

The geelbeck croaker is regarded as a highly palatable food fish. It is targeted throughout its range by commercial and recreational hook and line fisheries and it has been assessed as being overfished. South Africa has bag limits for recreational anglers and minimum size limits for both recreational anglers and commercial fishermen. They have also introduced quotas and marine protected areas. The population has severely declined and the
IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
has assessed this species as being
Near Threatened A near-threatened species is a species which has been Conservation status, categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature (IUCN) as that may be vulnerable to Endangered species, endangerment in the ne ...
.


References

{{Taxonbar, from=Q387470 Geelbeck croaker Fish described in 1830 Taxa named by Georges Cuvier