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Alectis alexandrina, commonly known as the African Threadfish, is a species of large marine fish in the jack family Carangidae. It is characterized by its deep, compressed body and, in juveniles, extremely elongated filamentous rays of the dorsal and anal fins. These filaments shorten considerably with age. It is a pelagic species found in tropical and subtropical waters of the eastern Atlantic Ocean and the Mediterranean Sea.
Physical Characteristics
- Body shape
- compressed
- Coloration
- Silvery-white to silvery-blue dorsally, fading to white or silvery on the flanks and belly. Juveniles may have faint vertical bands. Fins are typically hyaline (clear) to dusky.
- Scale type
- cycloid
- Mouth position
- terminal
- Distinctive features
- Deeply compressed, rhomboidal body shape, especially in juveniles., Extremely elongated, filamentous anterior rays of the dorsal and anal fins in juveniles, which can be several times the body length. These shorten significantly with age., Steeply rising head profile., Lateral line with a strong arch over the pectoral fin, becoming straight posteriorly., No scutes on the lateral line, a key differentiator from many other carangids.
- Dorsal fin
- Two dorsal fins; the first with 7-8 spines (often embedded in adults), the second with 1 spine and 18-20 soft rays. Anterior soft rays are greatly elongated in juveniles.
- Tail fin
- Deeply forked caudal fin.
- Pectoral fin
- Long, falcate (sickle-shaped) pectoral fins.
- Distinctive fins
- Anal fin with 2 detached spines followed by 1 spine and 15-17 soft rays. Anterior soft rays are greatly elongated in juveniles, mirroring the dorsal fin.
Identification Tips
Body Shape and Filaments
Look for the very deep, compressed body. In juveniles, the extremely long, trailing filaments from the dorsal and anal fins are unmistakable. These filaments are much shorter or absent in adults.
Lateral Line
Observe the lateral line; it has a strong arch anteriorly and becomes straight posteriorly, crucially lacking scutes (bony plates) which are present in many other Carangidae.
Head Profile
Note the steeply rising, almost vertical head profile, especially in larger individuals.
Coloration
The overall silvery coloration, often with a bluish tint dorsally, is characteristic. Juveniles may have faint dark bands.
Habitat
- Water type
- saltwater
- Depth
- Typically found from the surface down to about 100 meters (330 feet), though juveniles are often found in shallower coastal waters and estuaries.
- Environment
- Pelagic, inhabiting coastal and offshore waters, often near reefs, rocky outcrops, and sometimes estuaries. Juveniles are frequently found in shallower, turbid waters.
- Geographic range
- Eastern Atlantic Ocean, from Portugal south to Angola, including the Canary Islands and Cape Verde. Also present in the Mediterranean Sea, where it is considered a Lessepsian migrant (entering via the Suez Canal) but also has native populations in the western basin.
Aquarium Information
- Care level: advanced
- Temperament: semi-aggressive
- Diet: carnivore
- Minimum tank size: 1000 gallons (for adults)
- Temperature: 24-28°C (75-82°F)
- pH level: 8.1-8.4
- Hardness: 8-12 dKH
- Compatibility: Best kept in a species-specific tank or with other large, robust fish that can tolerate its active nature. Not suitable for reef tanks due to predatory nature.
- Special requirements: Requires a very large tank with ample swimming space. Excellent filtration and strong water movement are essential. Juveniles are often sold, but their rapid growth and eventual size make them unsuitable for most home aquariums. They are pelagic and need open water.
Wild Information
- Conservation status: least concern
- Seasonality: No distinct seasonality for spawning or migration across its entire range, though local aggregations may occur.
- Market price: Variable, generally moderate to high depending on region and size.
- Commercial importance: medium
- Taste: Mild, firm, white flesh
- Texture: Firm, flaky
- Cooking methods: Grilling, Baking, Frying, Steaming
- Nutritional value: Good source of protein and omega-3 fatty acids.
Key Facts
Juvenile Filamentsbehavior
The extremely long, trailing filaments of juvenile African Threadfish are thought to mimic jellyfish tentacles, providing camouflage and protection from predators.
Rapid Growthinteresting
African Threadfish grow very rapidly, especially in their juvenile stages, quickly outgrowing typical aquarium setups.
Lessepsian Migrantevolution
While native to the Eastern Atlantic, Alectis alexandrina has successfully colonized the Mediterranean Sea via the Suez Canal, demonstrating its adaptability.
Diet Shiftbehavior
Juveniles primarily feed on zooplankton and small invertebrates, while adults transition to a diet of small fish, cephalopods, and crustaceans.
Safety Information
Safe- Safety level: safe
- Venomous: No
- Edibility: edible
- Handling notes: No specific handling precautions beyond standard fish handling. Be mindful of sharp fin spines, especially the dorsal and anal spines, which can cause minor punctures. Large individuals can be powerful and should be handled with care to avoid injury to both fish and handler.
Similar Species
Indian Threadfish
Alectis indicus
A. indicus has a more widespread Indo-Pacific distribution. Morphologically, A. alexandrina typically has a slightly deeper body and a more steeply rising head profile. The number of soft rays in the dorsal and anal fins can also differ slightly, though this requires careful counting. A. indicus generally has 18-20 dorsal soft rays and 15-17 anal soft rays, similar to A. alexandrina, making geographic location a primary differentiator.
African Pompano
Alectis ciliaris
A. ciliaris (African Pompano) is found globally in tropical waters. While also having filamentous fins as juveniles, A. ciliaris typically has a more rounded, less angular body profile and often a more pronounced silvery-blue sheen. The number of dorsal and anal fin rays can also be used for differentiation (A. ciliaris typically has 18-20 dorsal soft rays and 15-17 anal soft rays, similar to A. alexandrina, but subtle differences in body depth and head shape are key).
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Actinopterygii
- Order
- Carangiformes
- Family
- Carangidae
- Genus
- Alectis
- Species
- alexandrina
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