Oysters are highly prolific. In one experi- 

 ment, a fennale 4-1/2 inches long released 

 about 70 million eggs in a single spawning. 

 Larger oysters can develop and discharge 

 more eggs. A female or male may spawn a 

 number of times. Most ripe oysters of both 

 sexes spawned after being stimulated to spawn 

 on 5 consecutive days. 



There was no significant difference in the 

 average number of eggs released during a 

 season whether the oysters were spawned at 

 3-, 5-, or 7-day intervals until they were 

 completely spent. Female oysters with larger 

 numbers of eggs at the beginning of the season 

 spawned more frequently than females with 

 fewer numbers. 



Until several years ago it was unknown 

 whether there is an age in the life of oysters 

 when they produce the best, most viable sexual 

 products. Recently, experiments with oysters 

 ranging inage from 2 to 30 or 40 years (fig. 4) 

 showed conclusively that there is no signifi- 

 cant difference in the quality of spawn devel- 

 oped by individuals of different ages or sizes 



and, therefore, mature oysters of all age 

 groups may be used safely as spawners. 



The oysters of the oldest group, some over 

 9 inches long and 4 inches wide, responded to 

 the spawning stimuli somewhat faster than 

 individuals of the youngest group. There was 

 no significant difference in the percentage of 

 fertile eggs because almost all eggs of all age 

 groups were fertilized. Moreover, the per- 

 centage of eggs developing to the straight- 

 hinge larval stage showed no variations that 

 could be ascribed to size or age of parent 

 oysters. Finally, no consistent difference 

 was found either in the size of the early 

 straight-hinge larvae developed from eggs 

 discharged by oysters of different age groups 

 or in survival and growth rate of these 

 larvae. 



Of special interest was the observation that 

 the sexes of the oldest oysters were about 

 evenly divided, thus contradicting the old, 

 often-expressed conception that females usu- 

 ally predominate among the oldest and largest 

 oysters. 



Figure 4. — Eastern oysters of different sizes and ages. The two smallest oysters are about 2 years old and the largest 

 are between 30 and 40 years of age. Regardless of the difference In sizes and ages of the oysters their spawn showed 

 equal viability. 



10 



