How to Identify Shortspine Thornyhead

To identify Shortspine Thornyhead (Sebastolobus alascanus), look at these key features.

Physical Characteristics

Body shape

compressed

Coloration

Typically reddish-orange to reddish-brown dorsally, fading to pink or whitish ventrally. Fins often have darker blotches or margins. Juveniles may exhibit more mottled patterns.

Scale type

ctenoid

Mouth position

terminal

Distinctive features

Large head with numerous prominent spines and ridges, particularly on the operculum and preoperculum., Large eyes, adapted for low light conditions., A deep notch in the dorsal fin between the spiny and soft-rayed portions., Pectoral fins are large and fan-like, often with a dark blotch at the base., The third dorsal spine is typically the longest, but shorter than the longest soft ray., The second anal spine is stout and longer than the third.

Dorsal fin

Single dorsal fin with a deep notch, typically 15-17 strong spines followed by 8-9 soft rays. The third dorsal spine is usually the longest.

Tail fin

Truncate to slightly emarginate caudal fin.

Pectoral fin

Large, fan-like pectoral fins with 20-24 rays, often extending beyond the anus.

Distinctive fins

Pelvic fins thoracic, with 1 spine and 5 soft rays. Anal fin with 3 spines and 4-5 soft rays; the second anal spine is notably robust and longer than the third.

Identification Tips

1. 1

   Head Spines

   Count the number and observe the prominence of spines on the head, particularly on the preoperculum and operculum. Shortspine Thornyhead has fewer and relatively shorter spines compared to Longspine Thornyhead.

2. 2

   Dorsal Fin Spines

   Examine the dorsal fin. The third dorsal spine is typically the longest, but it is shorter than the longest soft ray. This distinguishes it from Longspine Thornyhead where the third dorsal spine is longer than the longest soft ray.

3. 3

   Anal Fin Spines

   Note the relative lengths of the anal fin spines. The second anal spine is stout and distinctly longer than the third in S. alascanus.

4. 4

   Pectoral Fin Rays

   Count the pectoral fin rays (typically 20-24). The presence of a dark blotch at the base of the pectoral fin is also a helpful indicator.

5. 5

   Coloration

   Observe the overall reddish-orange to reddish-brown coloration, which can vary with depth and individual.

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