TEMPERATURE REQUIREMENTS FOR MATURATION OF GONADS OF NORTHERN OYSTERS

¹ U. S. Fish and Wildlife Service, Milford, Conn.

1. The temperature of 10.0° C. was not high enough to induce normal gametogenic activity in most of the oysters. Even the most advanced individuals of this group showed only slight development of the gonad after exposure to this temperature for 35 days. Apparently this temperature is near the biological zero for this activity.

2. Ripening of gonads and spawning of oysters of both sexes were achieved at a temperature as low as 15.8° C.

3. Wide individual differences in the extent of gonad development among the individuals constituting the same groups were commonly found.

4. In all temperature groups, ranging from 15.0 to 30.0° C., the physiologically ripe gametes were generally formed earlier in the males than in the females.

5. At 15.0° C. the most advanced males contained a few ripe spermatozoa on the 10th day. Fertilizable eggs were found on the 20th day and spawning was induced by the 35th day. At 20.0° C. oysters with ripe spermatozoa and fertilizable eggs were found on the fifth day. Spawning was induced on the 10th and 13th days in males and females respectively. At 25.0° C. ripe spermatozoa and fertilizable eggs were found by the fifth day. Spawning was induced on the seventh day. At 30.0° C. ripe spermatozoa and a few fertilizable eggs were found three days after the hibernating oysters were taken from their winter environment and placed at this temperature. Spawning was induced on the fifth day.

6. The average time at each of the experimental temperatures required for 50 per cent of the oysters to develop mature gametes was calculated to be:

[See formula in the PDF file]

To estimate the average time needed for development of mature gametes at temperatures intermediate to those given above, a simple curve is offered based on the equation:

[See equation in the PDF file]

where D is the average time needed, T is the temperature, and e is the base of the natural logarithms.

7. The quantity of glycogen in the oysters at the beginning of gonad development may control the quantity of spawn produced.