ARTIFICIAL PROPAGATION OF WHITEFISH, ETC. 27 



paint before using and one additional coat at the beginning of each 

 successive season. 



Where there is occasion to economize in the use of water, it may 

 pass through two or more troughs,' so phiced that the overflow from 

 the first trough is 8 inches higher than the head of the one immedi- 

 ately below. This fall gives some aeration to the water, and the 

 results are usually as satisfactory as where an independent water 

 supply is furnished to each trough. In this manner two double 

 troughs, with 38 compartments, occupying a floor space of about 90 

 square feet, with the required flow of 10 gallons of well-aerated 

 water per minute, will accommodate very nearly 3,000,000 eggs. 



If the water supply carries any considerable amount of sediment, 

 or if it is subject to even occasional periods of turbidity from sur- 

 face drainage or other causes, it is essential to install a filter, other- 

 wise the eggs soon become coated with sediment, the trays clog, and 

 the water circulation is impaired, a condition which is sure to result 

 in serious loss. The bureau has found that water pumped directly 

 from the lakes is the most satisfactory source of hatchery supply. 

 ISpring water, with its usually higher temperature, shortens the 

 natural incubation period and for this reason is objectionable. 



A convenience in caring for the eggs is a shallow picking trough 

 of any length, 15 inches wide and 2| inches deep. A strip one-half 

 by seven-eighths inch is nailed along each side of the bottom, and 

 upon these the trays rest, to give a good circulation while the eggs are 

 being assorted. The trough has a fall of not more than one-half inch 

 throughout a length of 20 feet, and it is fed by a flow of about 2 gal- 

 lons of water per minute. A dam at its lower end raises the water 1| 

 inches, not entirely covering the trays. This is a point that must not 

 be overlooked, for if the water flows over the tops of the trays many 

 of the eggs or fry will be washed away. 



CAKE OF EGGS AND FEY. 



On arrival at the hatchery the eggs are removed from the shipping 

 cases and turned into tubs, whence they are transferred to the hatch- 

 ing troughs. In removing them from the shipping trays to tubs the 

 method followed in washing eggs that have been held in cases for 

 several days is employed, the transfer being made at a temperature 

 not exceeding 50° F. 



The eggs are measured in a dipper having a perforated bottom, its 

 capacity first being determined by an actual count of eggs, 1 quart — 

 approximately G,400 eggs — being placed on each tray. A tray is 

 placed in the water and a dipperful of eggs poured upon it and 

 evenly distributed; then another tray, placed on top of the first, is 

 filled, and the operation repeated until 12 trays h'ave been filled. The 

 thirteenth, or cover tray, is left empty and the whole apparatus is 

 secured in place by the use of the cross bar or binder described on 

 page 24. For the first few weeks after the eggs are installed in the 

 hatchery they must be given close attention to prevent the growth 

 and spread of fungus; all dead eggs must be carefully removed and 

 the trays and troughs kept thoroughly clean. 



To remove the egg trays for assorting, the binder is first slipped 

 from the grooves and the trays are taken out separately. Each tray 

 will rise to the surface as the one above it is removed, or they may be 



