98 SALMONID^E. 



which they were bred^ although they do so, beyond doubt, in a 

 very great majority of instances; but it woukl appear from the 

 observations of Dr. Heysham and Sir WilUam Jardine, that if 

 they have roved to a very great distance from the estuary of 

 their own stream, they betake themselves to the mouth of the 

 first river they reach, if its temperature and the condition of its 

 waters suit them. 



Many Tweed Salmon are occasionally taken in the Frith of 

 Forth, and it is even said that in seasons when the Forth 

 fisheries are unusually successful, those of the Tweed are as 

 much the reverse. Sir Humphrey Davy is of opinion that the 

 taste of the waters of different rivers, according as they are 

 impregnated with different substances, and the effect produced 

 by them on the bronchise of the fish in the act of breathing, are 

 the guides by which the Salmon are led back to the streams to 

 which they have been accustomed ; and he accounts for their 

 being occasionally mistaken, by the fact that such mistakes 

 frequently occur during great floods, connected with storms, or 

 violent motion in the waters near the shore; by which the 

 components of the waters are disturbed, and their flavour con- 

 sequently altered. In confirmation of this view, he relates 

 that he " remembers in this way, owing to a ti'emendous 

 flood, catching with the fly a large Salmon which had mistaken 

 his stream, having come into the Bush, near the Giant's Cause- 

 way, instead of the Bann. No fish can be more distinct," he 

 proceeds, " in the same species, than the fish of these two 

 rivers, their length to their girth being in a ratio of 20"9 and 

 20-13." 



I am not, however, inclined to adopt this explanation. For 



