CHEAP FIXTURES FOR THE HATCHING OF SALMON. 961 



10.— CAPACITY OF THE TEOUGHS. 



The trays may be placed close together, allowing merely space enough 

 to admit the fingers when handling them. Each tray should receive a 

 single layer of eggs. They will count, of Atlantic salmon, about 2,000 per 

 square foot; of Schoodic salmon, about 1,800, and of California salmon, 

 about 1,200 per square foot. Allowing for all the waste space, a trough 

 ten feet long with a single series of trays will hold about 13,000 eggs,* 

 a very light stock. On two series of trays there would be 26,000 eggs — 

 a fair stock — and on three series of trays, 39,000 eggs. The latter num- 

 ber would give us, after hatching, about 4,300 alevins for every square 

 foot of trough-floor. With plenty of well-aerated water, a person with 

 some experience will have no difficulty in bringing as heavy a stock as this 

 through in safety. Indeed I have known a stock of over 5,000 per square 

 foot to be brought through without serious loss. If the fish would lie 

 evenly distributed over the floor there would be no difficulty, but at cer- 

 tain times they are seized with a perverse inclination to collect together in 

 heaps, and, if they remain so a long time, those underneath are suiFocated. 

 Therefore, though it is wonderful how much crowding they will endure, 

 the novice is advised not to attempt more than two series of trays, or 3,000 

 fish per square foot of trough. 



11.— SCREENS. 



If the trough is level there will be no occasion for any dams or barriers 

 until the eggs are hatched, but, as something of the sort is needed to keep 

 the alevins well distributed, it is better to provide for it in the beginning. 

 At regular distances, not more than five nor less than two feet apart, attach 

 to the opposite sides of the trough pairs of cleats, as if for a dam, such as 

 has already been described for the outlet. Connect these ojjposite pairs of 

 cleats by a low cross-piece or sill about half an inch high. As soon as the 

 fish begin to move about a fine wire screen can be slipped down between 

 the cleats until it rests upon the cross-piece ; this is shown near the lower 

 end of the front trough in Figure 5. The screen should not be coarser 

 than twelve wires to the inch, and finer still will be better. Wherever 

 dams occur in the trough or at its outlet the fish must be kept away from, 

 them by similar screens 

 placed a few inches above 

 the dams, or by one of 

 another pattern, shown in 

 Figure 12, which may be 

 termed a safety screen. 

 This form is worthy of 

 special recommendation. 



Fig. 13, 



61 F 



Eggs of Schoodic salmon referred to -when not otherwise specified. 



