Distinguished by the presence of large black spots on the back and on both lobes of the caudal fin; the young have no parr marks (Ref. 27547). Body fusiform, streamlined, somewhat laterally compressed; moderately, deeper in breeding males (Ref. 1998). Mouth terminal, normally very little oblique but greatly deformed in breeding males, with lower jaw enlarged, turned up at tip, mouth unable to close (Ref. 1998). Adipose fin large; pelvic fins with axillary process (Ref. 27547). Fish in the sea are steel blue to blue-green on the back, silver on the sides and white on the belly; large oval spots present on the back, adipose fin and both lobes of the caudal fin (Ref. 27547). Breeding males become dark on the back, red with brownish green blotches on the sides; breeding females are similar but less distinctly colored (Ref. 27547). Differs from Oncorhynchus mykiss
by having the following unique characters: anal fin with 11-15½ (usually 13½ ) branched rays; 177-240 scales in midlateral row; 26-33 gill rakers; large mature males with enormous hump; juveniles lacking parr marks; and lacking pink to red stripe on flank (Ref. 59043).