via The Atlantic Salmon Trust

which is the Atlantic Salmon, which is the Sea Trout ?

Adults-

Parr-

for me, the simplest method is to compare tails, markings around the lateral line and specially the corner of the mouth/eyeball relationship. this latter seems to be among experts the more sure-fire method as markings and fin shape may vary.

in short:
- salmon don’t have dots below the lateral line, have a pointed concave tail and the corner of their mouths stops around the center of their eyeball.
- the spots on brown trout extend below the lateral line, their tails are either flat or a ’rounded-off’ concave and the corner of the mouth extends past the eyeball. simple !

click either image for a full yet simple to remember explanation and other good to know groovy-fishy-slimey things like Salmon Facts and Sea Trout Facts.

as an aside-  although sporting very similar lifestyles, a Sea Trout is an anadromous (migratory) Brown Trout whereas a Steelhead is an anadromous Rainbow Trout.