Salmon (I) can be distinguished from large sea trout (II) by a more streamlined shape, concave tail, slimmer tail wrist, upper jaw reaching no further than rear of the eye, few if any black spots below lateral line, 10-15 (usually 11-13) scales counted obliquely forward from adipose fin to lateral line - trout have 13-16.
Salmon Sea Trout
General appearance Slender and streamlined More round and thickset
Head Pointed More Round
Position of the Eye Maxilla (bony plate usually alongside mouth)
does not extend beyond rear rear of eye Maxilla extends beyond eye
Colour Relatively few spots Often heavily spotted
Scale count (number from adipose fin to lateral line) 10-13 13-16
Fork of tail Usually forked Usually square or convex
Wrist of tail Slender Broader
Handling Easy to pick up by tail Tail slips through hand