182 SALMONID^ OF BRITAIN. 



FRESH-WATER TROUT. 



In the foregoing pages I have advanced reasons for supposing that we 

 jjossess only one species of sea trout, although our eastern and northern form of 

 salmon-trout, Salmo trutta, appears as a rule to have a few more ca^cal 

 appendages than the sewin, 8. camhricus, which is chiefly found on the southern 

 and western parts of England and Wales, and along most of our Irish shoi*es. 

 Externally so similar are these races, that no naturalist has yet succeeded in 

 pointing out unmistakable differences between the two, while their dentition 

 and the formation of the jaws vary to such an extent that they cannot be relied 

 upon as differentiating one from the other, although generally the vomer has 

 more teeth along its body in the northern than in the southern variety. 



Passing, as the sea ti'out does, by insensible gradations and almost unappreci- 

 able differences into the fresh-water races, it becomes necessary to make a rather 

 full investigation respecting whether such is the result of changing their 

 habitation from the sea to fresh waters or the reverse, or if their difierences are 

 the result of a hybridizing process carried on between an auadromous sea trout 

 and a non-migratoiy fresh- water species. 



As already observed (p. 143) Widegrcn, in 1863, asserted that the auadro- 

 mous sea trout and non-migratory fresh-water forms were simply varieties of 

 one common species, the diiferences in colour being consequent upon local 

 surroundings. Malmgren, in his account of the Salmonida3 of Finland, came to 

 the same conclusion, Collett, Norges FisJce, 1875, p. 167, likewise held an 

 identical opinion, so also did Malm in his Fauna, 1877, p. 538, Feddersen, 

 DanliseFerskvanrhfishe, p. 77, and others have likewise held and still maintain the 

 same views.* While Shaw, in 1843, gave a short account of having reared 

 sea trout from eggs and how some of the young, probably about a quarter, never 

 assumed the silvery niigi-atory livery, and he advanced the opinion that some 

 may permanently become residents in fresh water. But this question of the 

 identity of the marine and fi'csh-water forms has been already referred to 

 (pp. 144, 145). 



Opinions still are divided as to whether these two forms are merely divisions 

 of one species, but however this may be, ichthyologists are more agreed in 

 believing that all the varieties of our fresh-water trout are merely local races, in 

 which the differences in this very plastic form are brought about by their 

 surroundings. Differences which I have shown (p. 145) may disappear on the 

 young being raised under changed circumstances. 



J urine. History of the Fishes of the Lalce of Geneva, 1825, gave what he 

 believed to be sufficient reasons for considering tha.t the local forms existing 

 there and which had been accounted distinct species of trout, as Salmo trutta, 

 and S. fario, and were known under different names as the common trout, 

 salmon-trout, lake trout, river trout, al^^inc trout, &c., were all referable to 

 differences of sex, age, season, the natui-e of the water, food, light, &c. The 

 distinctive marks taken from the prolongation of the under-jaw beyond the 

 upper, the colour of the flesh, of the skin, with the size and shade of the sjwts, 

 the form of the tail, &c., being variable, were not to be depended on. 



Lunel remarking upon the various specific names that had been given to the 



* Dr. Gilnther, who in 1864 and at otlier times has given liis opinion that these views are the 

 outcome of the incapacity or ignorance of the observers, consistently omits all reference to 

 the subject in his Iiiiroduction to the Study of FUhcs, 1880, written according to the Zoolot/ical 

 Eecord in order "to serve as a book of reference to zoologists generally; and to supply those 

 \v'lio have frequent opportunities of observing fishes, with a ready means of obtaining informa- 

 tion." He also refrains from mentioning tliat some naturalists are unable to admit the numerous 

 species into which he has sub-divided trout. 



