460 
BULLETIN OF THE BUREAU OF FISHERIES 
RELATION OF TEMPERATURE TO SPAWNING 
The development and discharge of germ cells are well known to be functions of 
the water temperature. As was shown in table 1 and figure 7 the average temperature 
of the water in southern Puget Sound begins to rise in early spring from the winter 
minimum of about 6° to 9° C., reaching a level of 18° to 20° C. in August. During 
the early months of spring the gonads begin active development and the stored nour- 
ishment of the bodies is used in the maturation of the eggs and sperms. The extensive 
researches of Stafford (1913), Churchill (1920), Gutsell (1924), Nelson (1928a, b, c), 
Prytlierch (1929), Galtsoff (1930b, 1932), and others have demonstrated that there 
is a certain minimum, or critical temperature below which little or no spawning occurs. 
In Ostrea virginica this minimum is 20° C. for spawning by the female, although the male 
is able to spawn at a lower temperature. GaltsofFs observations are particularly sig- 
nificant, for he was able to show by laboratory experimentation that at a temperature 
of 20° C. or above, the sexually mature female may be induced to spawn by adding 
either sperms or sperm extract to the water. Below 20° C. sperms would not stimulate 
spawning. It is of importance to note that GaltsofFs work confirmed the conclusion 
of previous investigators based upon ecological observations. In the same manner he 
was able to induce spawning in the Japanese oyster, 0. gigas, by addition of sperms 
when the temperature was 25° C. or higher, although more recently Elsey (1933) 
wrote that spawning could be stimulated at 22° C. 
Orton (1920) stated that the European oyster, Ostrea edulis, spawns when the water 
temperature reaches about 60° F. (15° to 16° C.). In 0. lurida Coe (1931a) found 
specimens bearing larvae whenever the water temperature was as high as 16° C., 
while Hori (1933) set the minimum at 14° and the maximum at 20° C. The exactness 
of such observations is not always clear, however, for it is questionable whether the 
temperatures given are actually averages or merely approximations, and maxima and 
minima are not stated. 
Prytherch (1929), in his thorough study of various phases of the spawning and 
setting behavior of Ostrea virginica near Milford, Conn., concluded that spawning begins 
when the temperature at high tide reaches 20° C. He considered that the lower pH 
(7.2) of the water at low tide, when the temperature was much higher, was the factor 
preventing spawning. At high tide, on the other hand, when the water reached about 
20° C. and the pH was about 8.2 the oysters spawned. It is obvious that some factor 
in addition to temperature is necessary to stimulate spawning, and the suggestion 
that a high pH is required appears, from his results, to be well founded. Judging 
from these investigations, it is to be concluded that it is not the maximum tempera- 
ture on any particular day which must be up to the critical level, but the minimum, 
or high-tide temperature. 
It is clear, also, that the gonads must be at the required state of maturity before 
spawning will take place, regardless of temperature, for it was noted (Hopkins, 1931b) 
near Galveston, Tex., that the oysters were not ready to spawn during spring until the 
water temperature, after a rapid rise, reached about 25° C. At the same time, it 
has been well demonstrated that, with other factors favorable, spawning in 0. virginica 
begins when the high-tide temperature reaches the critical minimum of 20° C. It is 
important to know what conditions of temperature influence 0. lurida in this respect. 
(Hopldns, 1936.) 
A thermograph was placed on a frame in Oyster Bay so that the sensitive bulb was 
at the level of the oysters in the dike below. The records, therefore, represent with a 
high degree of accuracy the conditions of temperature of the water surrounding the 
