16 THE SCIENTIFIC ANGLER. 



within twelve months from the hatching period. Of their 

 rapid growth during the marine trip we have had ample 

 proof; this is perfectly rational, the sea being the feeding 

 ground for the whole family of migratory fish, the abun- 

 dance of small animalcule therein contained forming a 

 never-failing supply to the immigrants. 



In ascending rivers, salmon usually keep near one side 

 of the bottom of the water, but when their tributaries 

 are being ascended, they take the middle of the swiftest 

 streams. When a stream forms the outlet of a lake, or 

 any sheet of water known to be the annual resort of 

 migratory fish, it is of the most vital importance that no 

 obstruction be erected to arrest their passage. There has 

 been a considerable falling off in the takes of salmon 

 during the last twenty years or so. This may be attrib- 

 uted to three combined causes; (first) the erection of 

 weirs and flood gates; (second) river pollution; (third) 

 the depredation of the fungoid growth, termed the salmon 

 disease. 



With regard to the first and second causes here given, 

 we will take the particular case of the Trent. This river 

 was formerly one of the most important for salmon yields 

 in the United Kingdom, and it still ranks next to the 

 Thames for its yields of other fish. The river itself, 

 devoid of tributaries, is of the following extent : In Lin- 

 colnshire, twenty miles; in Nottinghamshire, fifty-five 

 miles; in Derbyshire, thirty miles; and in Staffordshire, 

 forty miles. The tributaries take their rise at fifteen 

 hundred to nineteen hundred feet above the sea level, 

 and are pure. They extend as follows: The Dove and 

 Ohurnet, sixty-three miles; Wye and Derwent, sixty-seven 

 miles; the Soar and Wreck (Leicestershire), sixty-five 

 miles, the Idle, forty-five miles; the Ely the and Anker, 

 thirty-five miles; the Terme, twenty-five miles; the 

 Tame, twenty-five miles; the Erewash, Sow (Stafford- 

 shire), and Devon river, each twenty miles. The whole 



