Brook Trout
  • Side view adult.
  • Side view adult.
  • Side view adult.
  • Top view of adult.
  • Bottom view of adult.
  • Head-on view of adult.
  • Close-up flank.
  • Close-up head.
  • Close-up mouth and snout.
  • Close-up tail.
  • Close-up dorsal fin.
  • Close-up anal fin.
  • Close-up pectoral fin.
  • Close-up pelvic fin.
  • The back shows light colored mottling ("vermiculations") on darker green background.
  • Close-up tail: Notice the presence of only a shallow fork.
  • Close-up anal fin: Notice the white leading edge, then black, then red.
  • The flank shows light spots on a dark background as well as red spots with blue "halos".
  • There are 23-55 pyloric caecae.
  • Underside of lower jaw: Each side of the lower jaw shows 7-8 mandibular pores.
  • Side view of a breeder: Notice the brighter colors and the yellowish belly.
  • Side view of a breeder: Notice the brighter colors, the yellowish belly, and the remnant parr marks.
  • Side view of a breeder: Notice the brighter colors, the dark green back, and the red belly.
  • Side view of a breeder: Notice the brighter colors, the dark green back and the red belly.
  • Bottom view of a breeder: Notice the white belly with two black lateral stripes surrounding it.
  • Flank of a breeder: Notice the bright colors, the yellow spots, and red spots with blue "halos".
  • Side view of a young-of-year: Notice the parr marks.
  • Side view of two young-of-year: Notice the parr marks.
  • Side view of two young-of-year: Notice the parr marks.
  • Side view of a young-of-year: Notice the parr marks on the flanks.
  • Alternate view of an adult.
  • Hybrid of brook trout X lake trout: Notice the intermediate appearance.
  • Hybrid of brook trout X lake trout: Notice the intermediate appearance.
  • Close-up tail of a brook trout X lake trout hybrid: Notice the intermediate appearance as well as the moderately forked tail with pointed caudal lobes.
  • Side view of a brook trout X brown trout hybrid: Notice the intermediate appearance.
  • Side view of a brook trout X brown trout hybrid: Notice the intermediate appearance.
  • Side view of a young-of-year hybrid of brook trout X lake trout: Notice the intermediate appearance as well as the parr marks.
  • Close-up anal fin of a brook trout X lake trout hybrid: Notice the intermediate appearance as well as the weakly developed black stripe after the white leading edge.
  • Close-up flank of a brook trout X lake trout hybrid: Notice the intermediate appearance as well as the sides with faint red spots; there are no blue "halos".
  • Close-up anal fin of a brook trout X brown trout hybrid: Notice the intermediate appearance as well as the white leading edge but no black stripe.
  • Close-up flank of a brook trout X brown trout hybrid: Notice the intermediate appearance as well as the irregular mottling on a bronze/reddish background.
  • Top view of a brook trout X brown trout hybrid: Notice the intermediate appearance as well as the weakly developed "vermiculations".
  • Intestines of a brook trout X lake trout hybrid: Notice the intermediate appearance; there are 65-85 pyloric caecae.
DescriptionSimilar Species
Family
Trouts (Salmonidae)
Body
Mouth and snout: Terminal, large and slightly oblique, with numerous small to medium-sized teeth on the upper and lower jaws. No barbels. Body patterning, color, and scales: Spots on side, mottling or irregular blotches on back (“vermiculations”); juveniles with thick dark vertical bars (“parr marks”). Background body color dark olive or dark gray on back and sides grading to cream, golden yellow, or pink on belly. Vermiculations lighter olive or gray; spots cream, light olive, yellow, light blue, and red. 210-244 cycloid lateral line scales. Dorsal and tail fins with lighter spots and vermiculations on a darker background; pectoral, pelvic, and anal fins with whitish edge, then a black stripe, and then clear or reddish coloration. Body shape and size: Body fusiform; oval in cross section. Typically 100-300 mm (4-12 in) TL; maximum about 510 mm (20 in).
Fins
Tail, dorsal and other fins: Slightly forked or squared tail. Single dorsal no spines and 10-14 principal rays. Pelvic fins abdominal with axillary process. Adipose fin present. Anal fin with 7-13 principal rays, usually 9.
Distinguishing Characteristics
The brook trout can be distinguished by its weakly forked to square tail, red spots on body on a dark background, pectoral, pelvic and anal fins with a thin white stripe on the edge followed by a black stripe, and then often reddish coloration, 9-12 gill rakers, and 7-8 mandibular pores on each side of the jaw. See also similar species information.
Breeding Adults
Colors become bright and pronounced, particularly in males. The back and sides are dark green, many of the spots on the sides are bright red, yellow, and blue, the upper sides of the belly are yellow-gold to bright red with dark black stripes enclosing bright white in the middle of the belly, and the chin is bright white or cream. The pectoral, pelvic, and anal fins are bright red, and the tail and dorsal fins are reddish brown. The lower jaw may become hooked in large males.
Juveniles
The young-of-year are dark brown on the back with 7-9 broad oval vertical bars (“parr marks”). Vermiculations and spots are inconspicuous. Older juveniles have more typical adult color and spotting patterns, but retain the parr marks.
Hybrids
Brook trout X lake trout (“Splake”), artificially produced in hatcheries and stocked in a few areas of the Great Lakes. Brook trout X brown trout (“Tiger trout), rare natural hybrid in Wisconsin; produced in hatcheries and stocked in 1970s.
Compare Similar Species
Tail Shape
Trout, BrookWeakly forked
Trout, LakeStrongly forked
Body Pattern
Trout, BrookRed spots
Trout, LakeNo red spots
Pectoral, Pelvic, and Anal Fin Pigmentation
Trout, BrookThin white stripe on the edge followed by a black stripe oftentimes with redish coloration
Trout, LakeNo stripes
Gill Rakers
Trout, Brook9-12
Trout, Lake12-24
Mandibular Pores
Trout, Brook7-8
Trout, Lake9-10
Similarity Index
Trout, BrookN/A
Trout, LakeVery similar
Comments
Trout, BrookModerately similar to other trout and salmon, but distinguishable by its pattern of light (or red) spots on a dark background
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