LABORATORY STUDY OF THE EFFECT OF LIGHT ON THE EMERGENCE BEHAVIOR OF 8 SPECIES OF COMMERCIALLY IMPORTANT ADULT PENAEID PRAWNS

The emergence behaviour of eight species of commercial prawns (between 25.0 and 30.0 mm carapace length) was studied in the laboratory. All except Penaeus merguiensis were nocturnal: they emerged from the subst ratum in the evening when the light was dimmed and buried themselves i n the morning, usually before dawn. P. merguiensis generally remained on the substratum during the day. The species can be grouped on the ba sis of their behaviour: the first group (P. plebejus and P. latisulcat us) was most sensitive to light, the second group (P. semisulcatus, Me tapenaeus ensis, P. esculentus, M. endeavouri and M. bennettae) was le ss sensitive to light, and the third (P. merguiensis) was least sensit ive to light. To find out what triggered emergence, two species (P. es culentus and P. plebejus) were exposed to different rates of light dim ming at dusk. Both species responded to absolute light intensity, but the response of P. plebejus was affected by the rate of change of ligh t intensity. The different responses of the species to different light intensities explains some of the differences in catchability in a mul ti-species prawn fishery.