458 
BULLETIN OF THE BUREAU OF FISHERIES 
SIZE OF BROODS 
Oysters have always aroused interest because of the very large numbers of eggs 
which they discharge. Various means of estimating the number of eggs spawned by 
an individual have been employed with highly divergent results. Galtsoff (1930a) 
gave a brief review of the literature on the subject and indicated that previous esti- 
mates for the average-size female of 0. virginica vary from about 9 millions to about 
60 millions. He made what is apparently the most thorough and accurate study by 
causing oysters to spawn and then making statistical counts of the eggs. He found 
that a female of 0. virginica discharged from 15 millions to about 114 millions in a 
single spawning period, and that after spawning had occurred the meat still contained 
a large quantity of eggs. During three periods of spawning one specimen of 0. gigas 
discharged a total of about 92 million eggs. The number of eggs spawned by a single 
individual throughout an entire season would be considerably greater than these 
counts. 
These species are of the oviparous type while the Olympia oyster is viviparous. 
In the waters of the United States are two viviparous species of oysters, 0. lurida, on 
the Pacific coast, and 0. equestris, described by Gutsell (1926) on the South Atlantic 
coast. The latter is too small to be of commercial use. 0. edulis, the European 
oyster, is also of this type and although the largest of the three it is much smaller 
than the common American oyster. Because of their small size the viviparous oysters 
cannot be expected to discharge the large quantities of eggs described above, but 
they have a considerable biological advantage in that every specimen is presumably 
capable of functioning each season as a female, while in 0. virginica only about half 
of the individuals are female. In the latter sex-change occurs, as recently studied 
by Coe (1932c, d), but not with the frequency found in the native oyster. The fact 
that the larvae are carried in the limited space of the branchial chamber in viviparous 
species would also appear to set a limit to the size of the broods. 
Moebius (1883) estimated, by an apparently satisfactory method, that the average 
brood of 0. edulis consists of about one million larvae. Stafford (1918) stated that 
the much smaller native oyster bears broods of about the same size, although his 
method of estimating the number is not clear. In order to establish with reasonable 
accuracy the number of larvae produced, counts were made of a number of broods. 
A gravid individual was carefully opened and the larvae rinsed from the gills 
and mantle. After killing them with formalin they were shaken in a measured quan- 
tity of water and exactly determined samples placed in a flat-bottom dish and counts 
made by means of a counting plate. Specimens of various sizes were used, though 
most of them were of market size. Counts were made of the separate broods of 13 
oysters, and on the mixed broods of 2 groups of 6 oysters. Table 12 gives the results 
and includes measurements of the shells of the maternal parents and the stage of 
development of the larvae in those broods which were separately counted. 
The average of all 25 broods is 214,642 larvae per oyster, although single broods 
varied from about 70,000 for the smallest specimen to 355,000 for one of the larger 
ones. These specimens were in general considerably smaller than those used in the 
two series of mixed broods, which represent more fairly the number of larvae pro- 
duced by the standard market-size oyster. The average of the Oyster Bay series is 
283,273 and of the Mud Bay series, consisting of somewhat smaller specimens, 247,199. 
The number of larvae produced obviously depends upon the size of the maternal 
individual and upon the degree of “fatness”, or amount of stored nourishment, which 
