56 Modern Fishciilturc in Fresh and Salt Water. 



FILTERS. If filters are necessary they may be made 

 in wide troughs with coarse wire screens at the upper 

 end and finer ones below, ending in cheese-cloth or flan- 



TK OUCH 



30 



PLAN OF HATCHERY WITH 12 TROUGHS; capacity 30,000 each in 

 single layer. A, sink for washing; B, closet; S, stove; 

 WW, windows. 



nel. Or the water may flow through sand and gravel, 

 according to the nature of the material to be filtered out. 

 There should be a screen at the head of each trough to 

 prevent stoppage at the outlet. 



CHAPTER III. 



TROUT EGGS. DISTINGUISHING SEX IN FISHES. 



It is with the fishes as with the birds : some species 

 show sexual differences at a glance at all times, some 



