How to Identify Threadfin Shad

To identify Threadfin Shad (Dorosoma petenense), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Silvery sides, darker bluish-gray to olive-green back. A distinct dark spot is present behind the upper operculum (gill cover). Fins are typically clear to dusky.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Elongated last ray of the dorsal fin (thread-like extension), Small, terminal mouth without teeth, Deeply forked caudal fin, Keeled belly with sharp scutes (ventral scales)

Dorsal fin

Single dorsal fin, with the last ray greatly elongated, extending posteriorly, often reaching or exceeding the caudal peduncle. Typically 10-13 soft rays.

Tail fin

Deeply forked caudal fin.

Pectoral fin

Relatively small, located low on the body.

Distinctive fins

The elongated dorsal fin ray is the most distinguishing feature.

Identification Tips

1. 1

   Dorsal Fin Ray

   Look for the long, thread-like extension on the last ray of the dorsal fin. This is the most reliable distinguishing feature from the Gizzard Shad.

2. 2

   Mouth Position

   The mouth is terminal (at the very front of the head) and relatively small, unlike the subterminal mouth of the Gizzard Shad.

3. 3

   Body Size

   Threadfin Shad are generally smaller than Gizzard Shad, typically reaching a maximum of 15 cm (6 inches) in length.

4. 4

   Dark Spot

   A distinct dark spot is present behind the upper operculum, though this can fade in preserved specimens.

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