VI TREFACE. 



that they all very commonly interbreed, but that the young revert 

 to one of the original parents. 



External form or colour, or internal organization (as the number 

 of cajcal ai^pendages), have been adduced as reasons for considering 

 certain trout as distinct species. In the following pages, however, 

 I. have brought forward instances which, I believe, show that all 

 these appearances are consequent upon local surroundings, and how 

 such ma}' be modified at will by changing the abode of the fish. 



That hybrids do occur among Salmonidte has been known in this 

 country for upwards of two centuries, and Sir James Maitland's 

 experiments distinctly prove that they may be fertile for, at least, 

 three generations, but time has yet to show for how long this will 

 continue, and, likewise, what the result of hybridization may be. So 

 far as investigations have gone they tend to demonstrate that hybrid 

 races do not revert to the original colours of either parent. 



Artificial fish breeding has given conclusive evidence that with 

 the maturity of the mother the size of the eggs of these fishes 

 augment, and that the progeny obtained from the largest ova 

 produce finer and more quickl}' -growing oiFspring than in such as 

 are raised from smaller eggs, or those given by younger or more 

 badly nourished mothers. This is a subject of great importance to 

 the fish-culturist, as showing that if he requires fine races pedigree 

 breeding must be resorted to ; and that skill, combined with ojjpor- 

 tunity, can produce far larger trout than can be obtained by simply 

 collecting eggs from these fish while living in their native streams. 

 It also tends towards the conclusion that a race may deteriorate 

 when they are the offspring of }'oung parents. 



Riparian proprietors jirobably may improve their local races by 

 the introduction of fresh blood, but when numerous small and 

 possibly lean trout are present in a stream or lake, such may be 

 consequent upon insufficiency of food caused by its absence or due 



