APPENDIX 



275 



THE SCALE FORMULA AND MOUTH TEST 



The difficulty of distinguishing small salmon from 

 large sea trout or parr from little trout used to be a 

 constant trouble to anglers, and I do not think even 

 experienced men felt quite happy about it till the 

 simple and easy tests of the size of scales and mouth 

 were suggested. The credit of this real piece of good 

 work belongs, I think, to that distinguished natural- 

 ist, Mr. G. A. Boulenger of the British Museum. He 



Scales of Sea Trout. 



Scales of Salmon. 



pointed out that the salmon had larger scales in 

 proportion to its body than the sea trout or trout, 

 and that a distinction between the species could be 

 made by counting the scales between the posterior 

 edge of the adipose fin and the lateral line forwards 

 in a transverse series. The salmon has from nine to 

 eleven scales in this position and the trout from 

 twelve to sixteen. The usual numbers are nine or 



