46 U. S. BUREAU OF FISHERIES. 



species in the same trough. Where supplementary trays are not 

 used the fry fall directly into the troughs. 



A trough 14 feet long will carry 56,000 eggs safely on four hatch- 

 ing trays in a single row, 14,000 eggs to the tray, but if it is necessary 

 to make more room a double row of trays may be put in, one tray 

 resting on top of the other. Thus the trough could contain 112,000 

 eggs as its full capacity. By inclining the trays as described above 

 a trough will carry this number up to the time of hatching. 



When the hatching stage arrives, two trays of 14,000 eggs each are 

 as many as should be left in one trough. With this number, by using 

 the horizontal sliding screen in the upper end and several spreaders 

 in the body of the trough at intervals of 2 or 3 feet, there is but 

 little danger of the alevins congregating and smothering in any 

 part of the trough. If it is necessary to hatch a much larger 

 number of fry in one trough, the sliding screen should be so arranged 

 that the water will fall well up toward or nearly against the end of 

 the trough. This is done by raising the screen and turning it back 

 against the supply trough. When danger from smothering has 

 passed, the screen is again laid flat. 



The spreaders are tin strips about 4 inches wide and 2 inches longer 

 than the width of the trough, and when placed in the trough they 

 are bowed toward the upper end, their excess length giving this 

 effect. Three " feet •' made of six penny finished nails are soldered to 

 the bottom, giving the spreader a half-inch clearance above the bot- 

 tom of the trough while the top extends just above the water level. 

 The current created by this device near the bottom of the trough 

 prevents the fry from congregating — a natural tendency — and serves 

 to keep them well spread on the bottom. 



The amount of water required for hatching and rearing depends 

 upon its temperature and the manner in which it is applied. It 

 should receive as much aeration as possible before entering the 

 troughs or ponds containing eggs or fish. At the Wythe ville (Va.) 

 station each molasses gate in the supply trough furnishes water for 

 two hatching troughs so placed that the water from the trough 

 nearest the supply falls about 8 inches as it enters the trough below. 

 In cleaning the higher troughs it is important that the plugs near 

 the outlet end be removed in order that any refuse may pass directly 

 into the drainage pipes. Under this arrangement eggs or fish in the 

 lower troughs develop and thrive equally with those receiving water 

 directly from the supply trough. 



The volume of water at a mean temperature of 53° F. generally 

 used in the troughs at this station, with their capacity for eggs and 

 young fish of varying sizes, is indicated in the following statement. 

 The figures given are for two troughs set end to end and supplied 

 with water from one gate as described above : 



Capacity of troughs : Gallons per minute. 



112,000 eggs 3^-4 



56,000 fry, up to feeding stage 5 



40,000 fingerlings, No. 1 to 1^ 5 



30,000 fingerlings. No. 1^ to 2 7 



20,000 fingerlings. No. 2 to 2i 8 



10.000 fingerlings, No. 2^ to 3 8 



6.000 fingerlings. No. 3 to 4 8 



