How to Identify Allis Shad

To identify Allis Shad (Alosa alosa), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Silvery flanks and belly, dark blue-green dorsal surface. Often has a distinct dark spot behind the operculum, sometimes followed by 1-7 smaller, less distinct spots along the lateral line.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Large, deciduous cycloid scales, Deeply forked caudal fin, Single dorsal fin located mid-body, Absence of a lateral line (typical for clupeids), A series of scutes (keeled scales) along the ventral midline, Large eye relative to head size

Dorsal fin

Single, relatively short-based dorsal fin, typically with 15-19 soft rays.

Tail fin

Deeply forked caudal fin, symmetrical lobes.

Pectoral fin

Relatively small, low-set pectoral fins, typically with 14-17 soft rays.

Distinctive fins

Pelvic fins are abdominal, located beneath the dorsal fin. Anal fin is long, with 19-25 soft rays.

Identification Tips

1. 1

   Body Shape and Coloration

   Look for a deep, compressed, silvery body with a dark blue-green back. The overall appearance is sleek and streamlined.

2. 2

   Dark Spot(s)

   The most reliable distinguishing feature is the presence of a prominent, dark, circular spot directly behind the upper part of the operculum (gill cover). Allis Shad may have additional, smaller, less distinct spots in a line behind the first, but these are often faint or absent. This differentiates it from Twaite Shad (Alosa fallax) which typically has 3-10 distinct spots.

3. 3

   Scales

   Allis Shad have relatively large, easily detached cycloid scales.

4. 4

   Mouth and Teeth

   The mouth is terminal. Unlike some other clupeids, adult Allis Shad typically lack teeth on the vomer and have very fine, deciduous teeth on the jaws, if any.

5. 5

   Gill Rakers

   A key internal identification feature for ichthyologists: Allis Shad have very numerous and fine gill rakers (typically 90-130 on the lower limb of the first gill arch), which are much more numerous and finer than those of the Twaite Shad (typically 35-60).

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