TEMPERATURE EFFECTS IN REPRODUCTION OF THE BAY SCALLOP, AEQUIPECTEN IRRADIANS LAMARCK

¹ Duke University Marine Laboratory, Beaufort, North Carolina

1. The events in the reproductive period of a population of bay scallops, Aequipecten irradians, have been analyzed from the beginning of gonad growth to the resting or neutral stage. The gonad index of field animals increased rapidly between May and early July, and the population reached a physiological state to commence spawning towards the later part of September. The spawning period covered approximately two months between September and November.

2. Gonad growth coincides with increasing temperature and peak phytoplankton production in early summer. The gonad index was maximum when the population was ready to commence spawning. The gonad index and the digestive gland index showed a reciprocal relationship during the reproductive period.

3. Scallops collected at intervals during the reproductive period were maintained at various temperatures in the laboratory, without food. The temperature effects on the events in the reproductive period have been studied.

4. Maintenance of scallops at various temperatures during the period of gonad growth resulted in a decrease in digestive gland and gonad indices. The oogonia and the oocytes were absorbed. The spermatocytes in the testis failed to mature.

5. Scallops with accumulated gonad reserves and developing oocytes in the ovary, when maintained at 20°, 25° and 30° C. rapidly matured and spawned. The scallops maintained at l0° C. and 15° C. failed to mature and spawn.

6. When the gonads were neutral, maintenance of animals at any of the experimental temperatures did not permit increase in gonad index or initiation of oogenesis. These animals had a high digestive gland index before they were introduced to the experimental temperatures.

7. The scallops with developing oocytes in the ovary, when maintained at 20° 25° and 30° C. in the laboratory, released gametes much earlier than the field population. The time required for release of gametes showed a direct relationship to temperature between 20° C. and 30° C.

8. The scallops maintained at various temperatures in the beginning of gonadal growth and gametogenesis survived longer than any other group maintained under similar conditions during the reproductive period. The animals in spawning condition were least tolerant to all the temperatures.