1. SALHO. '3 



Young specimens with dark cross bands ; the form of the caudal 

 fin changes with the age and sexual development X)f the fish, imma- 

 ture individuals having it more deeply emarginate. In males the 

 lower jaw is more developed than in females, and sometimes curved 

 upwards into a hook. 



Inbahitants of the fresh waters of the arctic and temperate parts 

 of the northern hemisphere, many species descending to the sea after 

 having deposited their spawn. 



There is no other group of fishes which offers so many difficulties 

 to the Ichthyologist, with regard to the distinction of the species as 

 well as to certain points in their life-history, as this genus. More- 

 over by far the greater portion of the voluminous literatiu"e on these 

 fishes consists of descriptions giving trivial or general characters only, 

 frequently confounding two or three species, or representing as species 

 what are, in fact, merely variations of sex, age, <kc. ; so that the task 

 of giving an account of all the species noticed by authors has not 

 been an easy one, and their history (in its present form must form 

 one of the most unsatisfactory portions of Ichthyology. 



The almost infixiite variations of these fishes are dependent oii 

 age, sex and sexilar development, food, and the properties of the 

 water. We shall subsequently see that at least some of the species 

 interbreed, and it is probable, although at present not confirmed by 

 direct observation, that such hybrids mix again with one of ^e 

 parent species, thereby producing an offspring more or less similar to 

 the pure breed. The coloration is, first of all, subject to variation ; 

 and consequently this character but rarely assists in distinguish- 

 ing a species, there being not one which would show in all stages 

 of development the same kind of coloration. The young of all the 

 species of this genus are barred ; and this is so «mstantly the case 

 that it may be used as a generic or even as a family character, not 

 being peculiar to Salmo alone, but aJ^o to Thymallus and probably 

 to Coregonus. The number of bars is not quite constant, but the mi- 

 gratory Trout have two (and even three) more than the River-Trout. 

 When the Sahnones haye passed this "Parr"-state,'the coloration 

 becomes mtich diversified. The males, especially during and imme- 

 diately after the spawning-time, are more intensely coloured and 

 variegated than the females, specimens which have not attained to 

 maturity retaining a brighter silvery coloiir, and being more similar 

 to the female fish. Food appears to have lees influence on the colo- 

 ration of the outer parts than on that of the fiesh : thus, the more 

 variegated specimens are frequently out of condition, whilst well-fed 

 individuals with pinkish flesh are of a more uniform though bright 

 coloration. Chemistry has not supplied us yet with an analysis of 

 the substance which gives the pink colour to the flesh of many Sal- 

 monoids ; but there is little doubt that it is identical with, and pro- 

 duced by, the red pigments of many Salt- and Fresh -water Crusta- 

 ceans which form a favourite food for these fishes. The water has 

 a marked influence on the colours: Trout with intense ocellated 



b2 



