MORTALITY IN PIKE-PERCH EGGS IN HATCHERIES. 9 
long standing in the handling of pike perch as well as many other 
species. Some of these species are known to stand such confinement 
fairly well, but many show various ill effects, such as hardening of 
the ovaries, wateriness of milt, and low percentage of hatched fry. 
Whatever the cause and physiological process involved, be it abnor- 
mal hydrogen ion concentration due to the crowding of the parent 
fishes, or more directly circulatory and nervous relations, the result 
is a degeneration of eggs and sperms. In the case of the pike perch 
especially the consequent mortality may, of course, fluctuate from 
year to year due to such causes as sudden changes of temperature 
(a sudden change of temperature is known to materially retard the 
ripening of the fishes in the pens) and weather conditions which 
may prevent pulling the nets and therefore postpone examination of 
the caught fishes. ‘Some specimens do not lay eggs even when ripe 
under such conditions. 
It may be of interest in this connection to give the opinions of men 
who have the supervision of pike-perch hatcheries which are located 
at Constantia, N. Y., Swanton, Vt., Put in Bay, Ohio, and Duluth. 
Minn. Their opinions, given in response to a letter of inquiry, are 
Fic, 23.—Eggs of Stenotomus prior to maturity. a, Normal egg; b, egg from a parent 
kept in a tank for two weeks. 
not based on numerical data but are the results of practical obser- 
vation. All of these four superintendents and a fifth, who was 
formerly connected with pike-perch work, agree that the mortality 
of eggs is proportional to the time that the adult pike perch are 
retained in pens and, conversely, that the percentage of hatched eggs 
from fish stripped when taken from the net is much greater than that 
of eggs from penned fish. Four of the men believe that both male 
and female are affected by penning, but that the female is more 
susceptible, while the fifth does not commit himself on this point 
but cautions against using the males more than once, i. e., on several 
days. 
earing more directly on the problem are some experiments made 
by the senior author in connection with some other work. Females 
of the common scuppaug (Stenotomus chrysops) were netted shortly 
before the spawning period and retained in a tank supplied with a 
continual fiow of fresh sea water. Specimen of these impenned fishes 
were dissected at intervals of a few days and the ovaries examined 
histologically. A progressive deterioration of the nearly ripe ova 
was observed, which at the end of two weeks had reached such a stage 
as shown in figure 28. 
