Alosa fallax (Lacep├Ęde, 1803)
Twaite shad
photo by Stergiou, K.I.

Family:  Clupeidae (Herrings, shads, sardines, menhadens), subfamily: Alosinae
Max. size:  60 cm SL (male/unsexed); max.weight: 1,500.0 g; max. reported age: 25 years
Environment:  pelagic-neritic; depth range 10 - 400 m, anadromous
Distribution:  Northeast Atlantic: Atlantic coasts from southern and western Iceland to northern Morocco (Ref. 188, 6683), including North Sea (Ref. 6683), Baltic Sea (Ref. 188, 6683); also Mediterranean Sea (Ref. 188, 3397, 6683) and Black Sea (Ref. 188, 3397, 26334). Several subspecies have been recognized based on the number of gill rakers and geographical location (Ref. 10541); some have since been given species-status (Ref. 59043). Listed in Appendix III of the Bern Convention (2002). Listed in Annex II and V of the EC Habitats Directive (2007).
Diagnosis:  Dorsal spines (total): 4-6; Dorsal soft rays (total): 12-16; Anal spines: 3-4; Anal soft rays: 16-22; Vertebrae: 49-59. Diagnosis: Body somewhat compressed, moderately deep with depth at pectoral fin less than head length, scutes apparent along belly (Ref. 188). Upper jaw notched, lower jaw fitting into it; no teeth on vomer; gillrakers fairly short and stout, total 30 to 80, shorter than gill filaments (Ref. 188). A dark spot posterior to gill opening, followed by 7 or 8 similar spots along flank, but sometimes faint or absent (Ref. 188, 40476). Alosa fallax resembles Alosa alosa, which has more and longer gillrakers and at most only 3 dark spots on flank (Ref. 188). Description: Body fusiform, a little compressed, the head wedge-shaped in cross-section; belly with a keel of scutes (Ref. 2945). Gill cover with radiating bony striae; gillrakers fairly short and stout, total 30 to 80, shorter than gill filaments; lower gill rakers 20 to 40 (Ref. 188, 2945). Upper jaw with a distinct notch to receive tip of lower jaw (Ref. 2945). Dorsal fin origin a little before midpoint of body; anal fin origin well behind dorsal fin base (Ref. 2945). Large, thin scales (Ref. 51442). Colouration: Deep blue dorsally, becoming greenish brown or golden on the sides and silvery ventrally; usually a series of 4-8 black blotches behind gill opening, sometimes a single blotch (Ref. 188, 59043, 88187).
Biology:  Amphihaline species (Ref. 51442), schooling and strongly migratory, but apparently not penetrating far up rivers (Ref. 188, 6683). Adults are usually found in open waters along the coast (Refs. 59043, 89486); juveniles are usually found along estuaries and near the shore (Ref. 59043), possibly making vertical diurnal movements synchronized with the tides; they remain in estuaries for over one year (Ref. 89630). Several landlocked (lake) non-migratory populations exist (Ref. 10541). Mostly anadromous, entering river mouths in March (Italy) or early June (northenr European rivers) to spawn in or above the tidal reaches; adults probably return to sea not long after spawning (Ref. 188, 6683). Eggs are demersal and widely scattered among sand or gravel on river bed (Ref. 118, 6683). Ichthyophagous, feeds on small fishes and crustaceans, the young taking the fry of herrings, sprats and gobies (Ref. 188, 51442). Females grow faster and are always larger than males of the same age (Ref. 10541). Very locally distributed due to pollution and impoundment of large rivers throughout Europe and most populations declined during the first decade of the 20th century, but seem to have stabilized at a low level since then (Ref. 59043). It has been suggested that members of the genus Alosa are hearing specialists with the American shad (Alosa sapidissima) having been found to detect and respond to sounds up to at least 180 kHz (Ref. 89631). This may aid in predator avoidance (e.g. cetaceans) (Ref. 89632). Hybridization between this species and the allis shad (Alosa alosa) has been reported from the Rhine (Ref. 89633) as well as rivers in France and Algeria (Ref. 10541). There is some evidence that indicates that shad hybrids may reproduce (Ref. 27567).
IUCN Red List Status: Least Concern (LC); Date assessed: 01 January 2008 Ref. (120744)
Threat to humans:  harmless
Country info:   
 

Entered by: Binohlan, Crispina B. - 17.10.90
Modified by: Boden, Gert - 08.05.18
Checked by: Binohlan, Crispina B. - 24.07.94

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