10 THE HABITS AND HAUNTS OF FISH. 



mature so quickly and grow so rapidly, when at 

 liberty, as to be able to descend to the sea 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 abundance of small animalculae therein con- 

 tained forming a never-failing supply to the immi- 

 grants. 



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 attributed to three 

 combined causes ; (ist) the erection of weirs and flood 

 gates ; (2nd) river pollution ; (3rd) 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 Lincolnshire, 20 miles ; in 

 Nottinghamshire, 55 miles; in Derbyshire, 30 miles ; 

 and in Staffordshire, 40 miles. The tributaries take 



