How to Identify Brook Trout

To identify Brook Trout (Salvelinus fontinalis), look at these key features.

Physical Characteristics

Body shape

torpedo

Coloration

Highly variable, but typically dark olive-green to brown on the back, fading to lighter flanks and a white belly. Distinctive vermiculations (worm-like markings) on the back and dorsal fin. Sides often display red or orange spots, some with blue halos (areolae), and numerous pale yellow spots. Pectoral, pelvic, and anal fins have a white leading edge, followed by a black stripe, and then reddish-orange coloration.

Scale type

cycloid

Mouth position

terminal

Distinctive features

Vermiculations (worm-like markings) on the back and dorsal fin., Red or orange spots, often with blue halos, on the flanks., White leading edge on pectoral, pelvic, and anal fins, followed by a black stripe., Lack of teeth on the shaft of the vomer (differentiates from true trout)., Adipose fin present.

Dorsal fin

Single, relatively short, with 10-14 rays, often mottled with vermiculations.

Tail fin

Slightly forked to square, especially in younger fish; becomes more square with age.

Pectoral fin

Paired, located low on the body, with a distinctive white leading edge.

Distinctive fins

Adipose fin present (a small, fleshy fin without rays between the dorsal and caudal fins).

Identification Tips

1. 1

   Coloration and Markings

   Look for the distinctive worm-like (vermiculated) patterns on the back and dorsal fin, and the red/orange spots (often with blue halos) on the sides. The white leading edge on the lower fins is a key identifier.

2. 2

   Tail Fin Shape

   The tail fin is typically square or only slightly forked, especially in larger individuals, distinguishing it from the more deeply forked tails of many true trout species.

3. 3

   Vomerine Teeth

   A definitive scientific distinction: Brook Trout (Salvelinus) lack teeth on the shaft of the vomer bone in the roof of the mouth, whereas true trout (Oncorhynchus, Salmo) possess them. This requires careful examination.

4. 4

   Absence of Black Spots

   Unlike many true trout (e.g., Rainbow Trout, Brown Trout), Brook Trout typically lack prominent black spots on their body or fins, though some dark spots may be present.

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