Sorites orbiculus specimens were subjected to a bleaching treatment in a laboratory experiment. The motility of the specimens was monitored by counting the number of specimens climbing the jar walls (climbing) and the specimens attached to the jar surface after tilting the jars (attached). To secure that motility was due to recent activity, the specimens were detached from the jar surfaces 18 h before the measurements. The observation was made on 14 jars containing 8 specimens and 5 jars containing 2 specimens per control/ treatment for 27 days. The treatment involved exposure to 5 µmol L-1 DCMU continuously and 0.19 mmol L-1 menthol during 6-hour incubation periods per day for 5 days per week over 27 days. Specimens were maintained in 120 ml of artificial seawater, with full water exchanges conducted twice daily, five days per week. In the final three days, specimens were incubated in the dark with only DCMU present. During the 18 h incubation periods, the weekends and the last three days, a Nannochloropsis food mixture was added. Control groups underwent identical conditions without the addition of bleaching agents. Environmental parameters were maintained at 26°C temperature, 37.5‰ salinity, and an illumination of 48 µmol photons cm-2 s-1 under a 12:12 h light-dark cycle.