MANUAL OF FISH-CULTURE. 97 



inclies lony; aud 15.J inches wide, and is provided with a waste-water 

 channel or shiiceway leading into the next compartment. In these 

 compartments are placed the hatching-boxes proper. 



The Clark box is 18 inches long, 14 inches wide, and 9i inches deep, 

 aud is made from f -inch dressed whitewood Inmber. On its nnder side 

 the box is provided with feet, li inches square and | inch thick, to allow 

 a free circulation of water under it and to prevent it from resting upon 

 any sediment or refuse that may be deposited on the bottom of the 

 tank ; and on the inside in each bottom corner is fastened a block, | inch 

 thick by 1^ inches square, to support the trays. Five circular oi^enings, 

 § inch in diameter, permit the escape of water from the box. A slot is 

 cut in one end of the box so that water from the compartment above 

 can not flow into the one below without falling into and passing through 

 this box. Upon the feet or risers inside the box rest 9 trays, made of 

 perforated zinc or fine wire netting, tacked upon a frame 16 inches long 

 aud 12 inches wide. This frame is made from finch pine, 1^ inches 

 wide. The trays are placed one upon the other in the box, the end 

 which contains the slot fitting snugly against the upper end of the com- 

 partment, in which is fitted a tin overflow. The whole is held in place 

 by a crossbar or binder, which fits in finch grooves cut in both sides 

 of the tank. The binder, resting upon the box, keeps it from rising in 

 the water, and is provided with feet so i)laced as to prevent the trays 

 from floating in the box itself. 



Upon the arrival of the green eggs at the hatchery they are trans- 

 ferred from the flannel trays to a large galvanized iron pan, and 

 thence to the Clark hatching-boxes. The eggs are measured with a 

 glass graduate and 5,000 placed upon each tray, the ninth or top tray 

 being used ouly as a cover. The eggs from domesticated brook trout 

 measure 350 to 450 per fluid ounce, depending on the age of the jish. 

 Eggs from wild trout collected in the Au Sable Eiver measure 450 to 

 the fluid ounce. 



CARE OF THE EGGS. 



At intervals of from three to six days during the period of incuba- 

 tion, in order to remove the bad eggs, the trays are taken from the 

 boxes and placed in a shallow picking-trough through which a stream 

 of not more than 3 gallons per minute is flowing. This trough is only 

 wide enough to allow perfect freedom in handling the trays when put- 

 ting them into or removing them from it, and only of sufficient depth 

 to allow the eggs to be fairly covered. Nailed to the bottom on each 

 side is a ^-inch strip, li inches wide, and running the entire length of 

 the trough. These strips permit the free passage of water beneath 

 the trays, as otherwise the water would flow over the tops and a great 

 many eggs would be lost. The bad eggs are removed with a pair of 

 tweezers, the labor of sorting being usually performed by girls, who in 

 time become so expert that one girl will often remove 100 bad eggs per 

 minute. 



F. C. 11. 1897 7 



