 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.
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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.
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Spot Characteristics | | Salmon, Atlantic | Usually few, covering upper sides; black & sometimes red present; nearly as large as pupil of eye; round, irregular ovals, or “X” shaped | | Salmon, Chinook | Moderate to numerous, limited to upper half of sides; black only; much smaller than pupil of eye; round or irregular in shape | | Salmon, Coho | Usually few, and limited to back and upper sides; black only; much smaller than pupil of eye; round or irregular in shape | | Salmon, Kokanee | Almost none, limited to upper back; black only; much smaller than pupil of eye; round to slightly oval in shape | | Salmon, Pink | Numerous and on both lobes, forming lines of elongated oval spots along rays | | Trout, Brook | Moderate to numerous; covering sides; cream, light, olive, yellow, red, sometimes with bluish halo; much smaller than pupil of eye; round | | Trout, Brown | Few 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, Lake | Many; covering sides; cream to light olive; much smaller than pupil of eye; irregular shape, much smaller than pupil of eye | | Trout, Rainbow | Many, covering most of sides; black only; much smaller than pupil of eye; round or irregular in shape | Tail Spots | | Salmon, Atlantic | Few or none, usually limited to base of tail | | Salmon, Chinook | Moderate to numerous and on both lobes | | Salmon, Coho | Few, limited to top of upper lobe | | Salmon, Kokanee | None | | Salmon, Pink | Numerous and on both lobes, forming lines of elongated oval spots along rays | | Trout, Brook | Few and lighter | | Trout, Brown | Few or none, usually limited to base of tail | | Trout, Lake | Numerous and on both lobes | | Trout, Rainbow | Numerous and on both lobes | Principal Anal Rays | | Salmon, Atlantic | 7-12, usually 9-11 | | Salmon, Chinook | 14-19 | | Salmon, Coho | 12-17, 1st ray elongated; fin distinctly falcate in YOY | | Salmon, Kokanee | 11-16, usually 13-14 | | Salmon, Pink | 13-19 | | Trout, Brook | 7-13, usually 9 | | Trout, Brown | 8-12, usually 9-11 | | Trout, Lake | 8-10 | | Trout, Rainbow | 8-12 | Lateral Line Scales | | Salmon, Atlantic | 109-121 | | Salmon, Chinook | 130-165 | | Salmon, Coho | 112-148 | | Salmon, Kokanee | 121-140 | | Salmon, Pink | 147-205 | | Trout, Brook | 210-244 | | Trout, Brown | 120-130 | | Trout, Lake | 185-210 | | Trout, Rainbow | 100-150 | Inside of Mouth in Breeders | | Salmon, Atlantic | White | | Salmon, Chinook | Black or dark gray | | Salmon, Coho | Black or gray; gums white | | Salmon, Kokanee | Dark gray with white mottling | | Salmon, Pink | Tongue and tip of jaw black or gray; gums white | | Trout, Brook | White on the teeth, tongue, and inside of mouth, but black on the gums | | Trout, Brown | White | | Trout, Lake | White | | Trout, Rainbow | White | Other Features | | Salmon, Atlantic | Branchiostegal 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, Chinook | Branchiostegal 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, Coho | Branchiostegal 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, Kokanee | Branchiostegal 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, Pink | Branchiostegal 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, Brook | Branchiostegal 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, Brown | Branchiostegal 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, Lake | Branchiostegal 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, Rainbow | Branchiostegal 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, Atlantic | Very similar | | Salmon, Chinook | Very similar | | Salmon, Coho | Very similar | | Salmon, Kokanee | Very similar | | Salmon, Pink | Very similar | | Trout, Brook | Moderately similar | | Trout, Brown | Very similar | | Trout, Lake | Moderately similar | | Trout, Rainbow | N/A | Comments | | Salmon, Atlantic | Not 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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