DEPOPULATION OF TROUT-STREAMS, 113 



as little as possible. They are easily injured, 

 easily killed ; and it is somewhat remarkable that 

 an injury, apparently slight, produces disease, one 

 of the symptoms of which is a whitish fungoid 

 growth that is, perhaps, infectious. Whenever 

 fry are transferred they should be poured from 

 tank to tank, and even, if practicable, into the 

 stream ; every sort of net for transferring should 

 be discarded. As a commercial commodity these 

 fish are exceedingly inexpensive. Robust fish 

 that have been feeding a month may be obtained 

 at as low a rate as two pounds per thousand, 

 and even less if great quantities are purchased. 

 In the case of fresh-water lakes, sea-lochs, or 

 rivers in which large fish already exist, it is 

 always advisable to turn in fry a mile or so 

 above the outlet, whence they will descend 

 in from eight to eighteen months. One of the 

 great secrets of success in turning down fry is 

 that the streams in which they are to begin 

 the battle of life are suitable to their re- 

 quirements. The stream, in the first place, 

 must be absolutely without pollution ; it must 

 have a clean gravel bed, with many little bays 

 and eddies. The young fish love to haunt 

 the bright, pebbly reaches, as these afford them 

 the greatest protection. The more thickly 

 grown the banks are with plants and trees, and 



