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 frJ^ 

 Whatever the cause and physiological process involved, be it abnor- 

 mal hydrogen ion concentration clue 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 isi 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, X. Y., Swanton, Vt., Put in Bay, Ohio, and Duluth. 

 Minn. Their opinions, given in response to a letter of inquiry, are 



Fig. 23. — Eggs of Stenotomus prior to maturity, a, Normal egg ; &, 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 Avas 

 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. 



Bearing 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 c/iri/sops) were netted shortly 

 before the spawning period and retained in a tank supplied with a 

 continual flow 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 23. • 



