16 U. S. BUREAU OF FISHERIES 
the mixture too thick, as the sand will not settle out, nor can the mixture be - 
sereened freely. This is poured through a screen placed across a washtub 
until the tub is full, when the débris is knocked off the top of the screen and 
another tub is filled. The partially clear water is poured off of tub No. 1, 
it is again filled with muck, and this is continued until there are a few quarts 
of muck of the consistency of cream in the bottom of the tubs. The tubs are 
next filled with water, which is agitated thoroughly, and then allowed 
to stand a few seconds to give the particles of sand time to settle. The 
contents of the tubs are then emptied into kegs or cans, when the water may 
be poured off in an hour or more. This leaves quite a thick mixture of even 
consistency, aS shown under the microscope. It should be free from sand, 
which would collect in patches in the bottom of the jars and interfere with 
the working of the eggs. 
It is very necessary that the muck be now thoroughly cooked or scalded, 
otherwise Infusoria will develop on the eggs, causing much inconvenience and 
some loss. Finally, the muck is drained off, dried in any desired form, and 
held ready for use. It should be prepared before the egg-collecting season 
begins. The screen is about 20 by 30 inches and is made by tacking to a 
wooden frame a fine wire cloth of 40 meshes to an inch. The finest mesh that 
will let small particles of muck through is best. The cloth is bagged down 
somewhat. with the tack heads up, in order to present a smoother surface for 
the quick cleaning of the screen. 
MORTALITY 
With most species of fish that have been propagated artificially 
it is possible to secure a high percentage of fertile eggs, and the loss 
during incubation is slight. Under ordinary conditions such losses 
are frequently, perhaps generally, less than 10 per cent. The eggs 
of the pike perch are an exception, and most fish-culturists no doubt 
would agree that a 50 per cent hatch is a successful one. 
This phase of fish culture frequently has been made the ground 
for investigation, but in all fairness it may be said that it has 
received but little detailed study and that no definite conclusion 
as to the causes of the unusually high death rate has ever been 
reached. The first cause of the remarkable mortality has been very 
generally ascribed by practical fish-culturists to failure of the eggs 
to fertilize, rather than to death of the eggs in the course of develop- 
ment. The assumption has been that a properly fertilized egg in- 
variably would segment and develop normally, but this assumption 
has not been supported by certain investigations. 
The methods of handling the brood fish and eggs are, in the main, 
very much alike at all stations where the pike perch is propagated. 
The less important details may vary to suit varying conditions or 
to meet the whims of the individual fish-culturist. It is highly 
probable that the admittedly crude but thus far unavoidable pro- 
cedure of adding and actively stirring foreign matter with the eggs 
to prevent cohesion results in their injury, and the necessity for the 
utmost care in the application of this treatment can not be empha- 
sized too strongly. Franz Schrader and Sally Hughes Schrader,® 
investigators for the Bureau of Fisheries, seem to disprove the 
theory that failure of impregnation is a direct cause of any large 
percentage of loss among pike-perch eggs. 
These investigators point out that in the artificial insemination of 
the pike perch the eggs are immersed in milt that is but slightly 

5 Mortality in Pike-Perch Eggs in Hatcheries. By Franz Schrader and Sally Hughes 
Schrader. Appendix V, Report U. S. Commissioner of Fisheries for 1922. Bureau of 
Fisheries Document No, 926, 11 pp., 23 figs, Washington, 1922. 
