How to Identify Sea Trout

To identify Sea Trout (Salmo trutta trutta), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

In freshwater, they resemble brown trout, with a dark brown to olive-green back, lighter flanks, and a cream to yellow belly, adorned with numerous dark spots (often with pale halos) on the back, flanks, and dorsal fin. When in the sea, they adopt a silvery-grey to steel-blue back, bright silver flanks, and a white belly, with fewer, less distinct spots. Upon returning to freshwater for spawning, they regain some of their darker, more spotted freshwater coloration, and males may develop a kype (hooked jaw).

Scale type

cycloid

Mouth position

terminal

Distinctive features

Adipose fin present (a small, fleshy fin between the dorsal and caudal fins)., Vomerine teeth present, typically in a zig-zag pattern., Large mouth extending beyond the posterior margin of the eye., Silvery coloration when at sea, reverting to more cryptic brown/spotted patterns in freshwater., Absence of distinct black spots on the caudal fin (unlike Atlantic Salmon).

Dorsal fin

Single, relatively short dorsal fin, typically with 10-14 rays. An adipose fin is present.

Tail fin

Slightly forked to almost square caudal fin, becoming less forked with age.

Pectoral fin

Paired pectoral fins, typically with 11-16 rays.

Distinctive fins

Pelvic fins are abdominal, located beneath the dorsal fin. Anal fin is relatively short, with 9-12 rays.

Identification Tips

1. 1

   Coloration

   Silvery-grey with few spots when at sea; brownish with numerous dark spots (often with pale halos) when in freshwater.

2. 2

   Caudal Fin

   Typically slightly forked to square, lacking the distinct black spots often found on the caudal fin of Atlantic Salmon.

3. 3

   Vomerine Teeth

   Arranged in a zig-zag pattern on the roof of the mouth, a key differentiator from Atlantic Salmon (which have a single row).

4. 4

   Maxillary Bone

   Extends beyond the posterior margin of the eye in adults, a feature often used to distinguish from Atlantic Salmon.

5. 5

   Spotting Pattern

   Spots are generally larger and more irregular than those of Atlantic Salmon, and often extend below the lateral line.

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