854 



SCANDINAVIAN FISHES. 



the rostral region), Avhich may be persistent in Salmon 

 normal in all other respects, and admits of quite a 

 considerable development (fig. 213). 



The Salmon leads a life full of changes, and it 

 ada])ts itself to tiiiini botii in form and colouring. The 

 form undergoes the same variations as in the Charr, 

 but is never so terete as it may sometimes be in the 

 latter. Most terete, most nearly fusitorin, though always 

 laterally compressed, is the true Salmon in its sea- 

 dress, with broad, convex liack and sometimes with 

 the greatest thickness of the body equal to two-thirds 

 of its greatest depth, which is then aliout one-fifth of 

 the length to the middle of the base of the caudal fin. 

 The difference from the Trout in the same dress is, 

 however, inconstant and sometimes absent; and in the 



Trout is, as a rule, more evident in the above respect: 

 it is generally easy to distinguish by the form young 



Salmun (lihnikla.r-forelh-y) from young Trout { fnrcJler), 

 the liod^' (jf the former being shallower, with tlie 

 greatest depth less than one-fiftli of the length. At 

 this stage, however, the difference is most marked in 

 the more or less forked shape of the caudal fin: in 

 young Salmon the length of the middle caudal rays is 

 less, in "\oung Trout move, than half that of the long- 

 est raj-s in the fin. As apjiears from the tal)le ot 

 averages on the preceding page, this character is in- 

 deed persistent, in typical specimens of the two varie- 

 ties, even in later life: l)ut it disappears in old Sal- 

 mon ^\•earing tlie spawning-dress, and sterile Trout 

 have a caudal fin most like that of typical Salmon. 





■■- ^'i^^'\~ f^ ,4^j^^.^i^^^ 



Fig. 2l?>. Moustrnus head (siiiioiis nialforniatiou) of a Salmo salar veiteviiensis, taken by Mr. Daiilgrkn' in If 

 ((, from the left; h. from in front. The specimen probably nieasnred 7 — 8 dm. 



■ ., of the natural size; 



Spawning-dress they both assume a deeper and thinner 

 form of body. This is especially prominent in old 

 males; which dui'ing the spawning- season develop, be- 

 sides the singular jaw-hook, to which we shall return 

 below, a high and more or less sharp dorsal projection 

 in front, supported internally by an indurated connec- 

 tive tissue. This hump, however, in no instance attains 

 the same development in the Salmons as in Charr of 

 the OnchorJii/nchiis group". Where tlie true Salmon 

 lives confined in fresh water, as in Lake Wener, it 

 also acquires as a general rule a deeper, more com- 

 pressed form; and that the Kelts (sjjcnt Salmon) have 

 a thinner body, we have already remarked. During 

 the earlier stai;'es the distinction between Salmon and 



Among the changes of growth tiiat most contri- 

 bute to modify the appearance of the Salmons, the 

 most striking are those which affect the form of the 

 snout. In j'oung Salmon the snout is comparatively 

 short and blunt; but its length sometimes increases 

 with age from about .S ?a'' to about 13 %' of that of 

 the body, or from aliout '21 %'' to 47 %'' of that of 

 the head reduced. Tiiis prolongation mainly affects 

 the anterior, prixMiasal part, the nostrils remaining at 

 a di.stance from the anterior orbital margin which in 

 young specimens is less, in old only slightly greater, 

 than the diameter of the eyes. The elongation pro- 

 ceeds uniformly in the females and the middle-sized 

 males, wliere the snout ac<|uires a moi-e or less point- 



" See Smitt, liiksvniseets iSalmonider, tafl. Ill, fig. 28. 



'' In Parrs. 



' lu the largest breeding niahs of the typical Salmon which we have been enabled to examine. 



