A comparison of the activity patterns of the sand goby Pomatoschistus minutus (Pallas) from areas of different tidal range

Abstract

Sand gobies (Pomatoschistus minutus) collected from beaches with a large tidal range (Scotland) exhibit a circatidal rhythm of activity in constant conditions in the laboratory. There is no endogenous circadian component to the rhythm. The phasing of the rhythm is such that peak activity occurs at the predicted time of ebb tide. Light‐dark (LD) cycles applied in the laboratory have a marked effect on activity greatly enhancing it at night so that the original tidal rhythm becomes nocturnal. Some evidence was obtained that LD cycles can entrain a weak nocturnal circadian rhythm in fish removed from tidal conditions. Contrary to expectations, some fish from beaches with a small and unpredictable tidal range (Oslofjord, Norway) also show a weakly persistent circatidal thythm without an endogenous circadian component, but great variability was noticed between individual fish. Laboratory LD cycles did not entrain a persistent circadian rhythm in the fish from the Oslofjord.