NATURAL HISTORY OF BRITISH SALMONID^. 159 



THE COMMON OR YELLOW TROUT 



{Salmo fario). 



This species, the mainstay and principal resource of the 

 fly fisher, is so well known, and is so widely distributed over 

 the whole of the British Islands, as to make any detailed de- 

 scription of its appearance or habitats superfluous. Indeed, so 

 far as the former is concerned, it would be practically impos- 

 sible ; as its colour and shape — except in the points already 

 referred to — are susceptible of infinite difference, and vary as 

 much as the qualities of the waters (whether in sources or 

 feeders), geological strata of the beds, and nature and quantity 

 of food found in the brooks, streams, rivers, ponds, lynns, 

 and lakes, where it is bred. 



Inhabiting such an infinite range of varying waters this 

 diversity of colouring is, in fact, a defence given by nature to 

 the trout for its preservation. Were its colour more uniform 

 or unchangeable, the fish would be so plainly visible in dif- 

 ferent waters or soils as to fall an obvious prey to its enemies, 

 whether biped or quadruped. In fact, experiments have shown 

 that the changes of colour are a question of minutes rather 

 than of days and weeks. Upon its transfer from a light to a 

 dark coloured vessel, or vice versa, the hue of the trout under- 

 goes an instant alteration, and in a very short time assimilates 

 itself more or less perfectly to that of its new domicile. Thus, 

 for instance, the trout of Lynn Ogwin, almost the whole bottom 

 of which is formed of grass, have, when first caught, a brilliant 

 emerald gloss over their golden and yellow tints ; and although 

 the waters are of the utmost clearness and the lake swarming 

 with fish, I was never able in any one instance to distinguish 

 these from their surrounding green. Again on the Spean 

 Water, Inverness, there are several small tarns in which I have 

 frequently taken fish almost the colour of ink ; yet these 

 tarns actually join the Spean, where many of the trout are of a 

 fine rich yellow — the cause of the difference being that the 



