270 THE RIVER-SIDE NATURALIST. 



Sir Humphry Davy, Preface to " Salmonia," 1828, says, 

 in writing of Loch Leven trout : " If trout from a lake or 

 another river of a different variety were introduced into 

 this river (the Teme), they would not at once change their 

 characters, but the change would take place gradually. 

 Thus I have known trout from a lake in Scotland, remark- 

 able for their deep-red colour, introduced into another lake 

 where the trout had only white flesh, and they retained the 

 peculiar redness of their flesh for many years. At first 

 they all associated together in spawning in the brook which 

 fed the lake, but those newly introduced were easily known 

 by their darker backs and brighter sides. By degrees, 

 however, from the influence of food and other causes, they 

 became changed ; the young trout of the introduced variety 

 had flesh less red than their parents, and in about twenty 

 years the variety was entirely lost, and all the fish were in 

 their original white state." No form of trout alters so much 

 from its original form as S. levcnensis when placed in other 

 waters. Examples have repeatedly come under our notice 

 where in the course of three years these fish have so 

 entirely changed that it would be difficult to recognise 

 them as the beautiful fish of the Fifeshire loch. Should, 

 however, repeated experiments and proportionate lapse of 

 time prove that the introduction of the Loch Leven trout 

 into our rivers does permanently improve the race (be- 

 lieving, as we do, that this trout is the descendant of the, 

 anadromous form), it will go far to confirm the assertion 

 of Widegreen, Collett, and others, " that there is only one 

 species of trout," and since advocated by Dr. Day, who 

 says " that he is unable to accept the numerous species 

 which have been described, believing those ichthyologists 

 more correct who have considered them modifications of 

 only one, which, as Salmo trutta, includes both the ana- 

 dromous and non-migratory fresh-water forms." 



