EEV. ME. WILLIAMSON'S OPINION. 137 



and what is its fate ? Before preparing to quit the river it had 

 suffered severely in strength, bulk, and general health, and, im- 

 prisoned in an atmosphere which had become unwholesome, it 

 soon begins to languish, and in the course of the season expires : 

 the experiment has been tried, and the result is well known. 

 This being an ascertained and unquestionable fact, is it a violent 

 or unfair inference that a similar result obtains in the case of 

 those salmon that are forced back, from whatever cause, to the 

 sea, that the salt-water element is as fatal to the pregnant fish 

 of autumn as the fresh-water element is to the spent fish in 

 spring ? , , . If there is any truth in these conjectures, 

 they suggest the most powerful reasons for resisting or removing 

 obstructions in the estuary of a river." The riddle of this double 

 migration of the salmon is likely still to puzzle us. It is said 

 that the impeUing force of the migratory instinct is, that the 

 fish is preyed upon in the salt water by a species of crustaceous 

 insect, which forces it to seek the fresh waters of its native 

 river ; again that while the fresh water destroys these sea-lice 

 a parasite infests it in the river, thus necessitating its return to 

 the sea. My own experience leads me to believe that salmon 

 can exist in the fresh water for a considerable time, and suffer 

 but little deterioration in weight, but they never, so far as I 

 could ascertain, grow while in the fresh streams. It is a well- 

 known fact that parr cannot live in salt water. I have both 

 tried the experiment myself and seen it tried by others ; the 

 parr invariably die when placed in contact with the sear-water. 



Mr. William Brown, in his painstaking account of The 

 Natural History of the Salmon, also bears his testimony on this 

 part of the salmon question : — " Until the parr takes on the 

 smolt scales, it shows no inclination to leave the fresh water. 

 It cannot live in salt water. This fact was put to the test at 

 the ponds, by placing some parrs in salt water — the water being 

 brought fresh from the sea at Carnoustie ; and immediately on 

 being immersed in it the fish appeared distressed, the fins stand- 

 ing stiff out, the parr-marks becoming a brilliant ultramarine 

 colour, and the belly and sides of a bright orange. The water 

 was often renewed, but they all died, the last that died living 

 nearly five hours. After being an hour in the salt water, they 

 appeared very weak and unable to rise from the bottom of the 

 vessel which contained them, the body of the fish swelling to a 

 considerable extent. This change of colour in the fish could not 

 be attributed to the colour of the vessel which held them, for 



