MORTALITY IN PIKE-PERCH EGGS IN HATCHERIES.* 
By Franz ScHraver, formerly lish Pathologist, U. S. Bureau of Fisheries, 
and 
SaLtity HucuHes Scuraver, Temporary Assistant, U. S. Bureau of Fisheries. 
The remarkable losses in the hatching of pike-perch (Stizostedion 
vitrewm) eggs have frequently made this phase of fish culture a 
ground for investigation. It is, however, not unjust to say that very 
little detailed study has been made and that no definite conclusion 
as to the causes of the high death rate has ever been reached. 
The methods used in the handling of parent fish and eggs are, in 
the main, very much alike at the various stations that hatch pike 
perch. The fishes are caught in nets that are usually pulled once a 
day, weather permitting. Those that are ripe are stripped immedi- 
ately, either in the field or at the hatchery, while the rest are retained 
in pens or live boxes. They are examined in turn daily until found to 
be ripe. In some years the sexes are found to be disproportionate in 
number. If males are scarce, the same individual may be used to 
obtain milt on several successive days. Fertilization is by the dry 
method, no water, or very little water, being used in the process. Milt. 
and eggs are stripped into a bowl in more or less regular alternation, 
and the whole is gently stirred at frequent intervals to insure the con- 
tact of the eggs with the sperm. When the bowl is sufficiently full— 
generally after 10 to 15 minutes—the contents are diluted with water 
which after a varying period is poured off and renewed until the eggs 
are contained in clear water. Cohesion of the eggs, which at this time 
are extremely sticky, is prevented by active stirring or by adding 
silt or starch to the water in addition to such mechanical agitation. 
Finally, after several hours, the eggs are put into the hatching jars 
through which a gentle current of water is kept flowing. 
As already indicated, the losses are very great. Nevin (1887) 
considers a hatch of 50 per cent’ a very fair success, and this would 
be agreed to by most fish-culturists. The cause of this great mor- 
tality is, in general, ascribed to failure of the eggs to be fertilized 
or else to injuries incurred while the eggs are being handled, espe- 
cially the active stirring and the addition of foreign materials to 
prevent cohesion. It seems almost certain that these last-named 
crude procedures—which so far are unavoidable—are very apt to be 
+ Appendix V to the Report of the U. 8S. Commissioner of Fisheries for 1922. B. F, 
Doc. No. 926. 
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