Nonparametric effects of monochromatic light on the activity rhythm of juvenile crayfish

The current study was carried out to test the influence of blue and red monochromatic light upon the motor activity rhythm of juvenile crayfish as well as determine whether this effect involves extraretinal photoreception. Two groups of 46 juvenile instars were used: (1) intact control animals and (2) animals lacking retina and lamina ganglionaris. All animals were individually monitored with a motor activity recording system for 30 days. For the first 10 days the animals were maintained and kept in constant darkness (DD) and then submitted to 24-h skeleton photoperiod cycles (SP) consisting of 30 min red or blue light signals calibrated to the same irradiance (25 Wm-2) during the next 10 days. Afterwards, they were left in DD for the last 10 days of the experiment. Activity was quantitatively and qualitatively analyzed. Results show that all control intact animals synchronized to blue or red light exhibited shift advances or delays. These results indicate that both circadian responses to monochromatic light investigated in this study are mediated by extraretinal photoreceptors.