Diagnosis: Salmo akairos differs from all other Salmo species and archaic trouts by the combination of contrasting black and white leading edges on dorsal and anal fins and the lack of dark spots on the sides of the body; high number of dorsal fin pterygiophores, 14-16 is distinctive, as other Salmo species and archaic trouts have modally 12-13; high number of gill rakers, 19-23, is also diagnostic with slight overlap in comparison with S. trutta often having a colour pattern on the fins similar to that of S. akairos (Ref. 55619).

Description: Snout variable but usually somewhat blunt in females, moderately acute in males; snout length slightly shorter than horizontal orbit diameter; mouth terminal or slightly inferior; maxilla plus supramaxilla long and thin with convex to straight upper margin, usually extending to vertical through posterior margin of orbit, slightly longer in males (Ref. 55619). Body very variable in depth, most specimens rather slender; fins large with acute tips in both genders (Ref. 55619). Number of pored scales in lateral line 104-111 (Ref. 55619). Gill rakers externally on the first gill-arch numerous and slender, 7-9 and 11-14 on upper and lower limb respectively; left side branchiostegals most commonly 12-13, right side 11-13 (Ref. 55619). Anal fin iv-v,8; dorsal fin v,11; pelvic fin i,7-9; pectoral fin i,12-13; pectoral fin appendage on both sides or on left side; caudal fin with modally 14 and 12-14 upper and lower procurrent rays respectively in addition to 19 principal rays (Ref. 55619). Two epurals, 4-5 expanded neural spines; vertebral count modally 56, 32-34 abdominal and 23-25 caudal vertebrae (Ref. 55619). Frontal not so broad at level of sphenotic, tapering anteriorly giving cranium a triangular shape from above; dermethmoid short and broad with a distinct posterior notch; premaxilla slender with small mesial pocket for the rostral cartilage; maxilla long and slender with small teeth and long weakly inflected premaxillary process; broad gap between palatine teeth and teeth on vomer head; vomerine longitudinal tooth row extending to posterior edge of vomer; glossohyal with five pairs of strong teeth; infraorbital 6 with an anterior protrusion (Ref. 55619).

Colouration: Dark violet parr marks, usually 10-11, discernible on side of body despite an overall dark colouration including different shades of brown and tint of green; sides of body ventrally lighter shifting from dusky yellow to dusky white; dorsal and anal fins with distinct white leading edges followed by black; this pattern, less prominent, also present on pelvic fin; dorsal fin also with numerous small black spots; side of head sometimes with single dark postocular blotch (Ref. 55619).