How to Identify Spiny Dogfish

To identify Spiny Dogfish (Squalus acanthias), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Dorsal surface is typically slate gray to grayish-brown, often with small, scattered white spots (more prominent in juveniles). Ventral surface is white or pale gray.

Scale type

placoid

Mouth position

inferior

Distinctive features

Two dorsal fins, each preceded by a sharp, ungrooved spine., No anal fin., Slender body., Five gill slits., Small, sharp, oblique teeth in both jaws., Nictitating membrane absent.

Dorsal fin

Two dorsal fins, the first larger than the second. Each has a prominent spine at its anterior margin.

Tail fin

Asymmetrical heterocercal caudal fin, with the upper lobe significantly longer than the lower lobe.

Pectoral fin

Triangular and moderately large.

Distinctive fins

Absence of an anal fin is a key diagnostic feature among sharks.

Identification Tips

1. 1

   Dorsal Spines

   The most definitive feature: two dorsal fins, each with a prominent, sharp spine immediately in front of it. These spines are ungrooved.

2. 2

   Absence of Anal Fin

   Unlike many other shark species, the Spiny Dogfish completely lacks an anal fin.

3. 3

   White Spots

   Juveniles and some adults exhibit small, scattered white spots along their flanks, though these can fade with age.

4. 4

   Body Shape

   A relatively slender, elongated body compared to many other shark species.

5. 5

   Size

   Adults typically range from 75 cm to 120 cm (2.5 to 4 feet) in length, rarely exceeding 150 cm (5 feet).

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