The effects of light adaptation on flicker fusion frequency were examined in the photoreceptors of 13 species of deep-sea crustaceans. Light adaptation produced a significant increase in the maximum critical flicker fusion frequency (CFF(max)) in 7 species-all 6 species of euphausiids in the study, and 1 species of oplophorid (Group 1). This is the first example of an increase in temporal resolution due to light adaptation in a deep-sea species. In the other six species-2 oplophorids, 1 pandalid, 1 pasiphaeid, 1 penaeid and 1 sergestid (Group 2)-light adaptation had no effect, or resulted in a decrease in the flicker fusion frequency. The mean dark-adapted CFF(max) of the Group 1 species was significantly higher, and the mean response latency significantly lower, than those of the Group 2 species. Possible explanations for these differences include the activity and bioluminescence mode of preferred prey items, as well as the retention of larval/juvenile adaptations in adult eyes.