How to Identify Brown Trout

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

Physical Characteristics

Body shape

torpedo

Coloration

Highly variable. Typically olive-brown to yellowish-brown on the back, fading to silvery-white on the belly. Sides are often marked with dark spots, some of which are surrounded by a lighter halo (red or orange spots are common, especially in riverine forms). Sea trout are generally more silvery with fewer, less distinct spots when in saltwater, becoming darker and more spotted upon returning to freshwater for spawning.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Adipose fin present (a small, fleshy fin between the dorsal and caudal fins)., Large mouth extending beyond the posterior margin of the eye., Vomerine teeth present on the roof of the mouth, typically in a zig-zag pattern or two rows., Absence of radiating streaks on the operculum (gill cover), distinguishing it from Rainbow Trout (Oncorhynchus mykiss)., Usually 10-14 rays in the anal fin.

Dorsal fin

Single, relatively short dorsal fin, followed by an adipose fin.

Tail fin

Slightly forked to truncate in adults, more deeply forked in juveniles.

Pectoral fin

Paired, located low on the body.

Distinctive fins

Adipose fin is a key salmonid characteristic.

Identification Tips

1. 1

   Spotting Pattern

   Look for dark spots, often with pale halos, and frequently red or orange spots on the flanks. The number and intensity of spots vary greatly.

2. 2

   Mouth Size

   The mouth extends noticeably past the posterior margin of the eye, a key differentiator from some other trout species.

3. 3

   Tail Fin Shape

   Adults typically have a slightly forked to square (truncate) tail fin, less deeply forked than many juvenile salmonids.

4. 4

   Absence of Opercular Streaks

   Unlike Rainbow Trout, Brown Trout lack the distinct radiating streaks on their gill covers.

5. 5

   Vomerine Teeth

   Careful examination of the roof of the mouth reveals vomerine teeth, usually in a zig-zag or double row pattern, which can distinguish them from Pacific salmon species.

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