Activity patterns of juvenile penaeid prawns in response to artificial tidal and day-night cycles: a comparison of three species

Activity patterns of Penaeus merguiensjs, P. esculentus and Metapenaeus endeavouri were studied in response to simulated tidal and day-night cycles in the laboratory. When these cycles were imposed separately, each species was more active at night and near the times of high tide. However, when the tidal and day-night cycles were imposed together, the relative strengths of the responses to the 2 factors differed among species. M. endeavouri was strongly influenced by the day-night cycle; virtually no activity occurred during the day but peaks of activity at night occurred near high tide. P. merguiensis and P. esculentus displayed some activity during the day with peaks around and just after high tide. However, for these 2 species, the peaks of activity near high tide at night were higher than the peaks during the day. All species were more active at night and, in the prawn's natural habitat, there is probably less risk of predation involved in being active at this time. Highest activity occurred near high tide and in the wild this is probably associated with feeding for all species. Decreased activity occurred at low tide, probably to avoid predation and, at times, dessication. The overall activity level of P. merguiensis was the highest of these species. The highest activity levels recorded for each species were similar but the lowest levels vaned markedly. M. endeavour; remained buried for many hours dur~ng the day, whereas the lowest mean activity levels recorded for P. merguiensjs were relatively high compared with the other species.