EVIDENCE FOR THE ENDOGENOUS CONTROL OF SWIMMING IN PINK SHRIMP, PENAEUS DUORAUM

¹ Institute of Marine Sciences, University of Miami, Miami, Florida 33149

1. Evidence that the swimming of migrating juvenile pink shrimp is under some measure of endogenous control was derived from experiments which indicated (i) that the pattern of swimming exhibited by a group of shrimp, maintained under constant conditions within a current of water, was similar over each of the two nights following their collection from nature, and (ii) that the swimming of two such groups, collected together, but maintained in separate current chambers within the laboratory, was similar during the night following their capture.

2. Endogenous control over swimming extended to the sign of rheotaxis which, during certain nights, in the absence of change in external conditions, would reverse in all shrimp at approximately the same time.

3. A predictable relationship occurred between the tide cycle to which the shrimp were exposed prior to capture and their subsequent swimming in the laboratory. The adaptive nature of this relationship is suggested from the fact that downstream swimming, which in nature occurs only during ebb tides and facilitates the offshore movements of juveniles, occurred in the laboratory only at the time of ebb tides in nature. It did not, however, occur at the time of all ebb tides but only during those occurring early in the evening.

4. It is suggested that the cohesion of the aggregations of migrating shrimp may largely be maintained by means of the synchrony imposed on the activities of all individuals by endogenous timing mechanisms.