28 U. S. BUREAU OF FISHERIES. 



taken out as a unit by encircling the stack of trays with a galvanized- 

 iron binder 1^ inches wide. All the trays are taken from one com- 

 partment and placed one after the other along the picking trough. 

 The dead eggs, which soon become white and opaque and are easily 

 distinguishable, are then picked out with small metal tweezers. If 

 allowed to remain on the trays, a fungus would soon develop on them 

 and spread its growth until all eggs within a short radius were af- 

 fected and eventually smothered. Wlien it is necessary to change 

 the position of the eggs, bringing those at the bottom to the surface, 

 it may be accomplished by the use of a soft feather, which, if care- 

 fully manipulated, will have no injurious effect. After carefully as- 

 sorting the eggs the trays are again placed in the hatching trough 

 and are looked over at least every three days during the first five or 

 six weeks. 



After the eggs have reached that stage of development where the 

 eye spots are discernible by the unaided eye they are comparatively 

 hardy and less susceptible to injury from handling. At this time it 

 is customary to remove them from the hatching trays and subject 

 them to a thorough washing. This may be accomplished by placing 

 the eggs in pans or buckets and passing a soft feather brush among 

 them; or a stream of water can be introduced into the vessel with 

 sufficient force to agitate the eggs to a considerable extent. This 

 washing not only removes all sediment that may have become at- 

 tached to the outer covering of the eggs, but it also causes all infertile 

 eggs (ringers), which up to this point have retained the color and 

 appearance of good eggs, to turn white, thus greatly facilitating 

 their removal. If there are only a few infertile or dead eggs, they 

 may be removed by the use of the tweezers mentioned; but if there 

 is a considerable number, their separation can be more readily accom- 

 plished by submerging the trays with the eggs in a salt solution. As 

 the specific gravity of dead eggs is slightly less than that of live ones, 

 they rise to the surface of the solution and may be removed with a 

 small net. The salt solution is composed of approximately one part 

 dairy salt to eight or nine parts of water. It is always advisable to 

 test its suitability by introducing into it a small number of both 

 living and dead eggs. Fresh water or salt may be added as required 

 to bring the solution to the proper density. 



From this time to the hatching point the eggs will require but 

 little attention, it being necessary to go over them only about once a 

 week for the purpose of removing any accumulation of sediment or 

 an occasional dead egg. 



From two to three weeks before the hatching period the eggs are 

 transferred from the trays to tubs of water, carefully washed, and 

 placed on clean trays, after which a careful measurement is made to 

 determine the actual number of eyed eggs remaining in the hatchery. 

 From this time until the fry commence to hatch a careful count is 

 kept of all the dead eggs removed. On the completion of the hatch- 

 ing period this number is deducted from the measurement of the 

 eyed eggs to determine the approximate number of fry. A careful 

 count is also kept of the fry losses up to the time they are ready to 

 plant. In a water temperature of 40° to 45° F. the eye spots are 

 visible in from 20 to 40 days, while the total incubation period is 

 approximately 131 days in a mean temperature of 36°. The fry 



