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Alosa alosa, commonly known as the Allis Shad, is an anadromous clupeid fish belonging to the family Clupeidae. It is characterized by its silvery body, large scales, and a distinctive dark spot behind the operculum, sometimes followed by a series of smaller spots. This species undertakes extensive migrations from marine environments to freshwater rivers for spawning.
Características físicas
- Formato do corpo
- compressed
- Coloração
- Dorsal side is dark blue-green, fading to silvery flanks and a white belly. Iridescent sheen, especially when freshly caught.
- Tipo de escama
- cycloid
- Posição da boca
- terminal
- Características distintivas
- Large, cycloid scales that are easily shed., A single, prominent dark spot behind the upper operculum, sometimes followed by 1-2 (rarely more) smaller, less distinct spots along the flank., Deep body, laterally compressed., Absence of a lateral line.
- Nadadeira dorsal
- Single, relatively short dorsal fin located mid-body, with 15-19 soft rays.
- Nadadeira caudal
- Deeply forked caudal fin, symmetrical lobes.
- Nadadeira peitoral
- Small, low-set pectoral fins.
- Nadadeiras características
- Pelvic fins are abdominal, located beneath the dorsal fin origin. No adipose fin.
Dicas de identificação
Body Shape and Size
Elongated, fusiform body, laterally compressed. Adults typically range from 40-60 cm in length, with a maximum recorded length of 70 cm and weight of 4 kg.
Coloration
Silvery flanks, dark blue-green back, and white belly. Often exhibits an iridescent sheen.
Spots
Presence of a single, prominent dark spot behind the operculum. This is a key differentiator from Alosa fallax (Twaite Shad), which typically has a row of 4-10 distinct spots.
Scales
Large, cycloid scales that are easily detached. The ventral keel is serrated.
Gill Rakers
Numerous and fine gill rakers (90-120 on the lower limb of the first gill arch), adapted for filter feeding on plankton. This is a crucial internal diagnostic feature distinguishing it from Alosa fallax (Twaite Shad) which has fewer and coarser gill rakers (40-60).
Habitat
- Tipo de água
- brackish
- Profundidade
- Typically found in coastal marine waters (0-200m) and estuaries, migrating into freshwater rivers for spawning.
- Ambiente
- Marine pelagic during feeding phases, anadromous, migrating into large, clear, fast-flowing rivers with gravel or sandy bottoms for reproduction.
- Distribuição geográfica
- Eastern Atlantic Ocean, from southern Norway and the Baltic Sea (rarely) south to Morocco, including the Mediterranean Sea (western basin) and its adjacent rivers. Historically present in many European rivers, but populations have declined significantly.
Informações sobre aquário
- Nível de cuidado: expert
- Temperamento: peaceful
- Alimentação: filter_feeder
- Tamanho mínimo do aquário: Not suitable for home aquaria due to its large size, migratory nature, and specific environmental requirements.
- Temperatura: 10-20°C (marine); 15-22°C (freshwater for spawning)
- Nível de pH: 7.0-8.5
- Dureza da água: Moderate to hard
- Compatibilidade: Not applicable for typical aquarium settings. In natural environments, they are schooling fish.
- Requisitos especiais: Requires large, migratory pathways between marine and freshwater environments. Not suitable for captivity.
Informações no ambiente natural
- Estado de conservação: vulnerable
- Sazonalidade: Spawning runs typically occur from April to June, depending on the geographic location and water temperature.
- Preço de mercado: Variable, often considered a delicacy in regions where it is caught.
- Importância comercial: medium
- Sabor: Rich, oily, and distinctive flavor, often compared to herring or mackerel.
- Textura: Flaky, tender, but with numerous small bones.
- Métodos de preparo: Grilled, Baked, Fried, Smoked
- Valor nutricional: High in Omega-3 fatty acids, protein, and vitamins D and B12.
Fatos principais
Anadromous Migratorbehavior
Alosa alosa is an anadromous species, meaning it spends most of its adult life in saltwater but migrates to freshwater rivers to spawn. This migratory behavior is crucial for its life cycle.
Spawning Behaviorbehavior
Spawning occurs at night, often accompanied by characteristic splashing and swirling at the water surface, a behavior known as 'shad dance' or 'fray'.
Filter Feederbehavior
Adult Allis Shad are primarily filter feeders, consuming zooplankton (copepods, cladocerans) and small crustaceans in marine environments, utilizing their numerous, fine gill rakers.
Conservation Concerninteresting
Populations of Alosa alosa have significantly declined across much of its range due to habitat degradation, pollution, overfishing, and barriers to migration (dams). It is listed as 'Vulnerable' by the IUCN.
Historical Importanceinteresting
Historically, Allis Shad was a highly valued food fish in many European countries, particularly France and Portugal, and its arrival in rivers signaled an important seasonal event.
Informações de segurança
Seguro- Nível de segurança: safe
- Venenoso: Não
- Comestibilidade: edible
- Observações de manuseio: No specific handling precautions are required beyond standard fish handling practices. They are not venomous and do not possess sharp spines that pose a significant threat. Their scales are easily shed, so handling should be gentle if the fish is to be released.
Espécies similares
Twaite Shad
Alosa fallax
Alosa fallax typically has a row of 4-10 distinct dark spots along its flanks, whereas Alosa alosa usually has only one prominent spot behind the operculum, sometimes followed by 1-2 less distinct ones. Internally, A. alosa has significantly more and finer gill rakers (90-120) compared to A. fallax (40-60).
Atlantic Herring
Clupea harengus
Atlantic Herring are generally smaller, have a more slender body, and lack the distinct dark spot(s) behind the operculum. Their scales are also smaller and less easily shed than those of Alosa alosa.
Classificação científica
- Reino
- Animalia
- Filo
- Chordata
- Classe
- Actinopterygii
- Ordem
- Clupeiformes
- Família
- Clupeidae
- Gênero
- Alosa
- Espécie
- Alosa alosa
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