ON THE ENDOGENOUS CONTROL OF TIDE-ASSOCIATED DISPLACEMENTS OF PINK SHRIMP, PENAEUS DUORARUM BURKENROAD

¹ Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida 33149

1. Swimming of both postlarval and juvenile pink shrimp was recorded in current chambers in the laboratory for three days following collection from nature.

2. In the apparent absence of environmental cues the animals maintained various forms of phase relationship with the tidal and diurnal cycles.

3. Postlarvae manifested a pattern of swimming, markedly in phase with the semi-diurnal tide cycle. Upstream swimming took place during flood tides and downstream swimming during ebb tides. No circadian periodicity was found and the confining of their activity in nature to night-time is considered a direct response to prevailing light intensity.

4. The patterns of swimming evidenced by juveniles differ depending, apparently, on some as yet undetermined aspect of the tide cycle to which they are exposed prior to collection. Individuals collected at times of new and full moon when ebb tides occur early in the evening, exhibit a different pattern of swimming from those of individuals collected at times of quarter moons when ebb tides occur late at night. The patterns obtained are clearly endogenous although their adaptive phasing with the tidal and diurnal cycles is not always evident.