Alectis alexandrina

Alectis alexandrina

The African threadfish (Alectis alexandrina Geoffroy Saint-Hilaire, 1817) is a fish belonging to the Carangidae family.

Systematic –
Eukaryota domain,
Kingdom Animalia,
Subkingdom Eumetazoa,
Phylum Chordata,
Subphylum Vertebrata,
Superclass Gnathostomata,
Class Actinopterygii,
Subclass Osteichthyes,
Superorder Acanthopterygii,
Order Perciformes,
Suborder Percoidei,
Family Carangidae,
Genus Alectis,
Species A. alexandrina.
The term is basionym:
– Gallus alexandrinus Geoffroy Saint-Hilaire, 1817.
The terms are synonymous:
– Alectis alexandrinus Geoffroy Saint-Hilaire, 1817
– Caranx alexandrinus (Geoffroy Saint-Hilaire, 1817);
– Caranx goreensis (Cuvier, 1833);
– Blepharis alexandrinus (Geoffroy Saint-Hilaire, 1817);
– Gallichthys aegyptiacus (Cuvier, 1833);
– Hynnis goreensis (Cuvier, 1833);
– Scyris alexandrina (Geoffroy Saint-Hilaire, 1817);
– Scyris alexandrinus (Geoffroy Saint-Hilaire, 1817);
– Selene goreensis (Cuvier, 1833);
– Vomer alexandrinus (Geoffroy Saint-Hilaire, 1817).

Distribuzione Geografica ed Habitat –
L’Alectis alexandrina è un pesce distribuito principalmente in tutto l’Oceano Atlantico orientale tropicale, abitando le acque dell’Africa occidentale dal Marocco all’Angola.
La specie ha avuto anche diversi individui prelevati soprattutto nella parte meridionale del Mediterraneo e una cattura estrema nel Mar Adriatico.
È una specie generalmente solitaria che vive, spostandosi con nuoto potente, lungo le acque costiere a profondità di 50-70 m, ma che può risalire in superficie o scendere fino a 100 m.

Description –
The Alectis alexandrina is a fish that can be recognized for having a very compressed and high body, in the shape of a large jack with sharp corners. As the body grows, it becomes more elongated. It reaches a maximum length of 100 cm, commonly 60 cm. Exceeds 3 kg in weight.
It has a silvery color, often with blue and greenish highlights and shades in the upper body and head. The fins may be silvery green or pale blue or jaline. In young individuals, there are sometimes 2-5 black zigazag bands on the upper body.
It has a wide mouth, and the teeth on its jaws are arranged in wide sets. The end of the upper jaw ends at the level of the anterior half of the eye. In the first gill arch there are 7-11 lower and 25-28 upper gill spines.
It is characterized by the obtuse profile of the head and a slight concavity at eye level. The dorsal profile is more curved than the ventral profile and the maximum height of the body is found between the origin of the soft rays of the dorsal fin and the soft rays of the anal fin.
Except for some parts of the head and body, it is covered in cycloid scales, apparently small, but by observing them carefully you notice that they are deeply embedded in the skin.
The lateral line, anteriorly, is very curved, but in the second part it becomes straight and carries 6-11(20) shields towards the caudal. At the base of the caudal fin, above and below the shields of the lateral line that runs along the peduncle, there are two keels on each side.
The dorsal fin is divided into two parts: the first part is made up of 5-7 spiny rays, which can be reabsorbed in larger specimens; the second part has 20-22 soft rays. The anal fin, almost symmetrical and similar to the dorsal fin, initially has 1 spiny ray (with age it is reabsorbed) and which is followed by 18-19 soft rays. The caudal is very forked and with pointed lobes. The pectoral fin, falcate, long and curved, extends beyond the junction point of the curved lateral line and the straight lateral line. Frequently in adults and juvenile stages the first ray of the dorsal fin and anal fin are very long and filamentous (in some juveniles the filamentous rays may be more). The pelvic fins are relatively long, more extensive in young specimens. There are 10 pre-anal and 16 post-anal vertebrae.

Biology –
Alectis alexandrina is a fish for which limited information on its biology is available, with the methods and characteristics of reproduction largely unknown, but observations on the similar species Alectis ciliaris suggest that individual fish can mate and then lay eggs.
The juvenile stages are pelagic and, drifting with the currents, can sometimes be found near river estuaries.

Ecological Role –
Alectis alexandrina is one of the three members of the genus Alectis and has a complex taxonomic history, characterized by two species 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 generic name Gallus which had been created by Lacépède.
The second description was made by Georges Cuvier in 1833 under the name Gallichthys a Egyptiacus. This name was also reevaluated twice, before the description was discarded as a junior synonym of A. alexandrina. The species has also been erroneously called Alectis alexandrinus. However the gender is feminine and therefore alexandrina is the correct spelling.
Adults are generally solitary in coastal waters, occupying the lower parts of the water column, down to at least 70 m. Juveniles are generally pelagic and drift with ocean currents, sometimes ending up in estuarine environments.
This fish feeds on squid and other fish.
The species is of minor importance to local fisheries throughout its range, and is also considered a good game fish, especially in the larger sizes. However, the species is rarely targeted by fishermen, due to its comparative rarity. The fish also fetches high prices in the market, unlike many other members of the trevally. The IGFA world record for the species is 8.10 kg caught off Daklha, Morocco in 1993.
The species is distributed along the coast of tropical Africa in the eastern Atlantic Ocean, extending to the Mediterranean Sea.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Louisy P., 2016. Guide to the identification of marine fishes of Europe and the Mediterranean. Il Castello Editore, Milan.

Photo source:
https://www.inaturalist.org/observations/41808220