Rainbow Trout
  • Side view adult.
  • Side view adult.
  • Side view adult.
  • Top view adult.
  • Bottom view adult.
  • Head-on view 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.
  • Close-up tail: The entire tail shows evenly spread spots.
  • Close-up anal fin: There are 8-12 principal anal rays; the anal fin shows few or no spots.
  • Underside of lower jaw: There are usually 9-13 branchiostegal rays on each side.
  • Inside of mouth of a breeder: Notice the white coloration.
  • Close-up head: The head region shows dark spots on light background with the spots being much smaller than the pupil.
  • Close-up dorsal fin: There are 9-13 principal dorsal rays; the dorsal fin shows numerous spots.
  • Close-up flank: The flank shows small dark spots on a light background, no red spots, and 100-150 lateral line scales.
  • The adipose fin is not edged in red; the anal fin is only slightly falcate.
  • Inside view: There are 27-80 pyloric caecae.
  • Inside of mouth: The vomerine teeth on the middle of the roof of the mouth are well-developed.
  • Side view of a breeding male: Males develop a bright red stripe and a hooked jaw.
  • Close-up flank: The flank of this specimen shows a steel-gray color and a faint red stripe.
  • Side view of a breeding female: Females develop a bright red stripe but no hooked jaw.
  • Side view of a breeding female: This female specimen was caught fresh from a lake full with eggs; the color is bright silvery and lacks the red stripe.
  • Side view of a breeding male: This male specimen shows a dark steel-gray color with reddish hues along the lateral area.
  • Side view of a breeding male: This male specimen shows a dark steel-gray color with reddish hues along the lateral area.
  • Side view of a breeding male: This male specimen shows a dark steel-gray color with reddish hues along the lateral area.
  • Close-up head of a breeding male: Males develop a hooked lower jaw, a steel-gray head, and reddish opercles.
  • Side view of a breeding male: Males develop a hooked lower jaw, a steel-gray head, and reddish opercles.
  • Side view of a yearling: Yearlings still show parr marks.
  • Side view of a young-of-year: Notice the well-develop parr marks.
  • Side view of tow young-of-year: Notice the parr marks.
  • The inside of mouth shows a lack of pigment (white color).
  • Alternative side view of an adult.
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, with an obvious broad red to pink lateral stripe in inland populations; juveniles also with oval dark vertical bars (“parr marks”). Inland populations are densely spotted with a background of dark olive or green on the back, silver, bronze or olive on the sides, and cream below, with a broad, red, rose, pink, or purple lateral stripe. In Great Lakes fish the background color is gray-blue or greenish-blue on the back and silvery on the sides and the red stripe is often faint and sometimes absent. Spots dark brown or black; round or irregular in shape, substantially smaller than the pupil of the eye. 100-150 cycloid lateral line scales. Dorsal and tail fins tan, olive, or gray; both usually spotted throughout. Pectoral, pelvic, and anal fins tan, olive, or gray, usually without spots. Adipose fin spotted but not edged in red or orange. Body shape and size: Body fusiform; oval in cross section. Inland typically 300-400 mm (12-16 in) TL, maximum about 550 mm (22 in). Great Lakes typically 500-700 mm (20-28 in) TL; maximum about 800 mm (32 in).
Fins
Tail, dorsal and other fins: Slightly forked to square tail. Single dorsal fin with no spines and 10-12 principal rays. Pelvic fins abdominal with axillary process. Adipose fin present. Anal fin with 8-12 principal rays.
Distinguishing Characteristics
The rainbow trout can be distinguished by its pattern of dark spots on a light background. See also similar species information.
Breeding Adults
Males develop a hooked lower jaw. Inland, the red lateral stripe may be slightly more pronounced and the body more steel-gray than greenish. Great Lakes populations become dark steel-gray on their head, back, and fins and the lateral stripe is a dull dark red or purple.
Juveniles
Have 5-10 oval vertical bars (“parr marks”) on sides.
Hybrids
None known from Wisconsin.
Compare Similar Species
Spot Characteristics
Salmon, AtlanticUsually few, covering upper sides; black & sometimes red present; nearly as large as pupil of eye; round, irregular ovals, or “X” shaped
Salmon, ChinookModerate to numerous, limited to upper half of sides; black only; much smaller than pupil of eye; round or irregular in shape
Salmon, CohoUsually few, and limited to back and upper sides; black only; much smaller than pupil of eye; round or irregular in shape
Salmon, KokaneeAlmost none, limited to upper back; black only; much smaller than pupil of eye; round to slightly oval in shape
Salmon, PinkNumerous and on both lobes, forming lines of elongated oval spots along rays
Trout, BrookModerate to numerous; covering sides; cream, light, olive, yellow, red, sometimes with bluish halo; much smaller than pupil of eye; round
Trout, BrownFew to many, covering most of sides; both black and red present; nearly as large as pupil of eye; round or irregular ovals in shape
Trout, LakeMany; covering sides; cream to light olive; much smaller than pupil of eye; irregular shape, much smaller than pupil of eye
Trout, RainbowMany, covering most of sides; black only; much smaller than pupil of eye; round or irregular in shape
Tail Spots
Salmon, AtlanticFew or none, usually limited to base of tail
Salmon, ChinookModerate to numerous and on both lobes
Salmon, CohoFew, limited to top of upper lobe
Salmon, KokaneeNone
Salmon, PinkNumerous and on both lobes, forming lines of elongated oval spots along rays
Trout, BrookFew and lighter
Trout, BrownFew or none, usually limited to base of tail
Trout, LakeNumerous and on both lobes
Trout, RainbowNumerous and on both lobes
Principal Anal Rays
Salmon, Atlantic7-12, usually 9-11
Salmon, Chinook14-19
Salmon, Coho12-17, 1st ray elongated; fin distinctly falcate in YOY
Salmon, Kokanee11-16, usually 13-14
Salmon, Pink13-19
Trout, Brook7-13, usually 9
Trout, Brown8-12, usually 9-11
Trout, Lake8-10
Trout, Rainbow8-12
Lateral Line Scales
Salmon, Atlantic109-121
Salmon, Chinook130-165
Salmon, Coho112-148
Salmon, Kokanee121-140
Salmon, Pink147-205
Trout, Brook210-244
Trout, Brown120-130
Trout, Lake185-210
Trout, Rainbow100-150
Inside of Mouth in Breeders
Salmon, AtlanticWhite
Salmon, ChinookBlack or dark gray
Salmon, CohoBlack or gray; gums white
Salmon, KokaneeDark gray with white mottling
Salmon, PinkTongue and tip of jaw black or gray; gums white
Trout, BrookWhite on the teeth, tongue, and inside of mouth, but black on the gums
Trout, BrownWhite
Trout, LakeWhite
Trout, RainbowWhite
Other Features
Salmon, AtlanticBranchiostegal rays usually 11-12, principal dorsal rays 11-12, adipose fin not edged in red, pyloric caecae 40-74, gill rakers 15-20, vomerine teeth poorly developed, dorsal fin with few or no spots
Salmon, ChinookBranchiostegal rays usually 13-19, principal dorsal rays 10-14, adipose fin not edged in red, pyloric caecae 140-185, gill rakers 16-26, vomerine teeth well developed, dorsal fin spotted
Salmon, CohoBranchiostegal rays usually 11-15, principal dorsal rays 9-12, adipose fin not edged in red, pyloric caecae 45-114, gill rakers 18-25, vomerine teeth well developed, dorsal fin with few or no spots
Salmon, KokaneeBranchiostegal rays usually 13-14, principal dorsal rays 11-13, adipose fin not edged in red, pyloric caecae 50-87, gill rakers 29-43, vomerine teeth well developed, dorsal fin with few or no spots
Salmon, PinkBranchiostegal rays usually 9-15, principal dorsal rays 10-15, adipose fin not edged in red, pyloric caecae 95-224, gill rakers 24-35, vomerine teeth well developed, dorsal fin with few or no spots
Trout, BrookBranchiostegal rays usually 9-13, principal dorsal rays 10-14; adipose fin not edged in red, but dark margin in young; pyloric caecae 23-55; gill rakers 9-12; vomerine teeth well developed; dorsal fin spotted
Trout, BrownBranchiostegal rays usually 10, principal dorsal rays 9-11, adipose fin often edged in red, pyloric caecae 30-60, gill rakers 14-17, vomerine teeth well developed, dorsal fin spotted
Trout, LakeBranchiostegal rays usually 10-14, principal dorsal rays 8-10, adipose fin not edged in red, pyloric caecae 93-208, gill rakers 16-26, vomerine teeth well developed, dorsal fin spotted
Trout, RainbowBranchiostegal rays usually 9-13, principal dorsal rays 10-12, adipose fin not edged in red, pyloric caecae 27-80, gill rakers 16-22, vomerine teeth well developed, dorsal fin heavily spotted
Similarity Index
Salmon, AtlanticVery similar
Salmon, ChinookVery similar
Salmon, CohoVery similar
Salmon, KokaneeVery similar
Salmon, PinkVery similar
Trout, BrookModerately similar
Trout, BrownVery similar
Trout, LakeModerately similar
Trout, RainbowN/A
Comments
Salmon, AtlanticNot native; stocked in the past without estabishing a population. Occurs only in the Great Lakes as a rare stray from other states and Ontario.
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