SPAWNING AND EGG PRODUCTION OF OYSTERS AND CLAMS

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Abstract
The total number of eggs released by individual female oysters, conditioned in midwinter, ranged from 10,000 to 66.4 million, and averaged 28.8 million. Females that developed gonads under natural conditions in early summer released from 23.2 to 85.8 million eggs for an average of 54.1 million eggs per female. The highest number released by any female at a single spawning was 48.8 million. This single heavy release exceeded the seasonal total egg discharge of all but 7 of the 43 females in the experiment. There was no significant difference in the average number of eggs released whether the females were spawned at 3-, 5-, or 7-day intervals. The average number of spawnings per female decreased progressively as the length of time between spawnings increased. The total number of eggs produced showed a correlation of 0.54 (significant at 0.01 level) with the size of the female, as indicated by shell cavity volume. There was also a correlation of 0.51 (significant at 0.01 level) between the number of eggs released and the number of spawnings, i.e., females with a great number of eggs to release spawned more frequently than those with fewer eggs. No correlation could be found between the number of eggs produced and Polydora or sponge infestation, or shell injury. No 2- to 5-day refractory period was found, as reported by earlier investigators. Both male and female oysters can spawn every 24 hours, until their supply of mature gametes is depleted. The total number of eggs released by individual female clams ranged from 8 million to 39.5 million, and averaged 24.6 million per clam. The highest number released by any female at a single spawning was 24.3 million. The correlation between the number of eggs and shell cavity volume was .38 (significant at .05 level). There was no significant difference in the average number of eggs per female whether spawned at 3-, 7-, or 14-day intervals, nor was there any significant difference in the average number of spawnings per female. The correlation between number of spawnings and number of eggs produced was not significantly different from zero.