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 palatine and vomer; gillrakers fairly short and stout, total 30 to 80, shorter than gill filaments (Ref. 188, 59043). Usually a series of 4-8 black blotches behind gill opening, but sometimes a single blotch, the others faint or absent (Ref. 188, 40476, 59043). 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 (Ref. 2945). Dorsal profile curved (Ref. 59043). Gill cover with radiating bony striae; gillrakers fairly short and stout, total 30 to 80, as long as or shorter than gill filaments; lower gill rakers 20 to 40 (Ref. 188, 2945, 59043). 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; dorsal fin with 4-6 unbranched and 12-16 branched rays; anal fin with 3-4 unbranched and 16-22 branched rays; pectoral fin with 15-17 rays; pelvic fin with 1 unbranched and 8 branched rays (Ref. 2945, 89637). Large, thin cycloid scales; 54-71 scales on a longitudinal line; 16-20 transverse scales; scales regularly arranged on flank (Ref. 51442, 59043, 89637). Belly with a keel of scutes; 18-23 pre-pelvic scutes and 12-18 post-pelvic scutes, a total of 32-41 scutes (Ref. 2945, 89637).

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).