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 
I 
