A Field Guide to the Atlantic Salmon

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Salmon or sea trout?  Fresh fish or well-mended kelt?  Coloured or takeable fish?  This handy field guide answers these and other questions you may have when fishing for atlantic salmon.

Salmon or sea trout?

One of the most frequently asked questions from newcomers to salmon fishing.  And until you have seen a few telling them apart can seem tricky.  Head Bailiff Willie Farndale once apprehended a chap with a sea trout on the shingle and a book between his knees trying to work out if this was his first salmon.  The fish had travelled a thousand miles, leapt two waterfalls and run three wears to get to that shingly bank and it lay there gasping.  Its not that important; let it go.  Do your homework before you get to the bank.  Run through some back issues of the copiously illustrated magazine Trout & Salmon.  Without looking at the captions see if you can tell whether you're looking at a salmon or sea trout. 


The following diagnostic table provides some simple rules of thumb:                                                            

  • General Appearance     

Salmon is torpedo shaped.  Sea Trout are rounder.  

  • Head 

Salmon have a pointed head.  Sea Trout a blunter head.  

  • Eye 

In salmon the rear of the eye lies within the maxilla - the bony plate next to the mouth.  In Sea Trout the maxilla extends beyond the rear of the eye.

  • Tail                                 

Salmon have a forked tail.  Sea Trout have a flat or even convex tail. 

  • Scale Count                    

Salmon have 10-13 scales between the adipose fin - the little one at the top between the dorsal fin and tail - and the lateral line.  Sea Trout have 13-16 scales.

  • Wrist of Tail                   

The salmon has a slender wrist to the tail.  The Sea Trout has a broader wrist.  

  • Handling                         

The salmon is easy to pick up by the tail.  The Sea Trout tail tends to slip through the hand.

  • Anal Fin                          

In the salmon, when closed, the innermost ray of the anal fin is closest to tail.  In the Sea Trout it is the outermost ray of the anal fin that is closest to the tail.     

Salmon or Grilse?

A grilse is a salmon returning to the river after just one year at sea.  Size is the best indicator although not totally reliable.  Generally a grilse will be between 3-10lbs in weight.  A two season salmon will generally be into double figures. 

Fresh fish or well-mended kelt?

After breeding through the back end of the year surviving salmon will lose their breeding colours and return to their more familiar silver colouration and return to the sea.  However, these post-breeding fish or kelts, are usually long and thin.  These fish are released and allowed to return to the sea before they return to breed in another season.

Fresh Run or Coloured Fish?

After a few weeks in the river salmon soon lose their characteristic silver colouring and turn a dull grey colour.  In addition the males, or cock fish, develop a pronounced kype on the lower jaw used to stimulate the female, or hen fish, and in aggressive exchanges with other cock fish. 

In addition, the males often develop characteristic red spots leading to their description as a red, coloured, stale or tartan fish.  These fish have been in the river long enough for the transition into their breeding colours to have begun and they are usually released by anglers to allow them to breed.

If In Doubt?

Salmon, sea trout, kelt or coloured?  If in doubt let the fish go.  



Finally, if you found this Guide useful can you let me know by voting for it - see below.  And let me know if you would like to see any additions or further improvements.

Catch fish, Dennis.


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Many thanks to the Atlantic Salmon Trust for kind permission to reproduce illustrations from their excellent pamphlet Atlantic Salmon Facts - the little blue book as it is affectionately known!  Copies can be obtained by writing to: Atlantic Salmon Trust, 3/12 King James Vi Business Centre, Friarton Road, Perth PH2 8DG, Scotland.

Some Useful References

Sutterby, R. & Greenhalgh, M.  2005  The Atlantic Salmon: An Illustrated Natural History  Merlin Unwin Books

Superbly illustrated modern classic.

Falkus, H. & Greenhalgh, M.  1997  The Salmon & Sea Trout Fisher's Handbook  Excellent Press.

A 'Haynes Manual' of Salmon Fishing with the addition of two of Falkus' finest pieces of prose capturing the magic of both salmon and sea trout fishing.

Lendrem, D.W. 2007  Field Guide To The Atlantic Salmon  Fishers of Rothbury.

Handy A5 reference guide with illustrations of the Atlantic Salmon.


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