MANUAL OF FISH-CULTURE. 79 



Four liatching-trays are placed in each trough and are secured by 

 key.s or wedges, aud shouhl be from 1 to 2 inches lower at the end next 

 to the head of the trough, as shown at D, D, D, D, page 78. If placed 

 in this way, each tray will hold from 12,000 to 15,000 eggs with safety. 

 Muddy water during- the hatching season necessitates the use of a tin 

 tray witli a perforated bottom (shown at E, page 78), which is 13f inches 

 wide and 32 inches long. This sets inside of the hatching-trough on 

 feet raising it an inch above the bottom of the trough. The hatching- 

 tray containing the eggA is placed inside and rests on the brackets 

 shown at G. The fish, as they hatch out, fall from the hatching-tray 

 upon the perforated bottom of the tin tray, aud by their movements 

 ■work the sediment through, leaving them on a clean bottom and in no 

 danger of being smothered. The tin trays are also useful in counting 

 fish, or in holding small lots of fish of different species in the same 

 trough. Where supplementary trays are not used, the fry fall directly 

 into the troughs. 



Troughs 15 feet long will admit of four hatching-trays in a single 

 row, each of which will safely carry 12,500 eggs, making 50,000 to a 

 trough; this is enough to work easily, but if it is necessary to make 

 more room a double row of trays may be put in, one tray resting on 

 the top of the other. Thus the trough could contain 100,000 eggs as 

 its full capacity. The troughs will carry this number up to the time 

 of hatching by placing the trays lower at one end than the other, as 

 previously descri'bed. 



When the batching stage arrives, two trays of 12,500 eggs each are 

 as many as should be left in one trough ; with this number, by using the 

 horizontal sliding-screeu in the upper end, 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 than this in one trough, 

 the sliding-screen is so arranged that the water falls well up against 

 the end of the trough. This is done by raising the screen and turning 

 it back against the reservoir, or by putting in a wedge shaped block for 

 the water to fall upon, turning the thin side of the block toward the 

 upper end of the trough. Fifty thousand trout have been hatched in 

 one trough prepared in this way without loss from suffocation, but it is 

 not advisable to hatch such a large number together. 



Tlie amount of water necessarj^ for hatching and rearing depends 

 upon the temperature and the manner in which the water is applied. 

 The water should receive as much aeration as possible before entering 

 the comijartments containing the fish aud eggs. At Wytheville, where 

 there is an even temperature of water of 53° in the hatchery, about the 

 following quantities are used in the troughs containing fisli and eggs: 



100,000 oggs during mcnbation, 12i gallons per minute. 

 100,000 fish hatching to time of feeding, 30 gallons per minute. 

 100,000 fish from 1 to 4 months old, 50 gallons per minute. 

 100.000 fish 4 to 6 months old, 100 gallons per minute. 

 100,000 fish from 6 to 12 months old, 200 gallons per minute. 



