24 Modern Fishculture in Fresh and Salt WateV. 



you put a dam across it, tap it at one side and make the 

 ponds on that side, well guarded by a ditch, so that no 

 surface water can get into the ponds or increase their 

 flow. 



As the "shells" of fish eggs do not contain lime, soft 

 water is as good as hard for their culture. 



THE POLLUTION OF WATERS. 



Ordinary house sewage does not seem to affect fish 

 either in health or flavor. The Hudson River is one 

 vast sewer for such large cities as Troy, Albany, Hud- 

 son, Poughkeepsie, Newburg, Sing Sing, Peekskill, 

 Yonkers and New York, as well as of hundreds of 

 smaller places, yet the shad and salmon run to the dam 

 at Troy and are as healthy and fine flavored there as 

 those caught below. It is difficult to poison a great river 

 like the Hudson. I don't mean to say that these fish 

 would live in the sewers ; far from it ; but the fact is that 

 the sewage comes in at the sides of the river, is soon di- 

 luted, precipitated and rendered harmless. This is not 

 the case with many chemicals, nor with sawdust. 



Sazvdust. There is a popular idea that sawdust kills 

 off the trout in a stream by clogging the gills of the fish. 

 Such a thing might have happened, but a trout is not 

 killed by sand in its gills. The great harm that saw- 

 dust does is by smothering the spawning beds, more or 

 less, and in impregnating the water with turpentine 

 from pine and tannin from oak, which destroy the trout 

 while in the egg. See the chapter on hatching troughs 

 and the impossibility of hatching trout in troughs of 

 raw, new wood. 



Chemicals of many kinds will kill any and all fish if 



