EXPERIMENTAL STUDIES ON THE PHOTOTACTIC REACTION OF PORTUNID(PORTUNUS TRITUBERCULATUS (MIERS)) IN HORIZONTAL PHOTOGRADIENTS

Phototaxis was manifested when portunid were placed under horizontal photogradients of 10^-4-10² lux illumination.The phototactic reaction increased with increasing light intensity and reached its maximum within 10^-3-10^-2 lux region (when the water temperature was 15.0-16.5℃).The phototactic reaction decreased beyond the bounds of 10^-2 lux.The background light influences photoaxis of portunid in horizontal photog-radients,but phototactic reaction were essentially the same whether the portunid was on background light or not,with the exception that the reaction in the former case was weaker Than that in the latter one.when phototactic reaction was high,the influence of background light on portunid became less.The influence was greater if the reaction was weaker.The phototactic reaction of portunid under background light was raised,when the intensity of artificial light source was increased within certain bounds.