The temporal characteristics of the visual systems of eight species of mesopelagic crustaceans were studied using the electroretinogram (ERG). Experiments were conducted on shipboard, using dark-captured specimens collected off the south coast of Cuba. As one would expect based on the relative intensity differences in their light environments, the deepest living species, Systellaspis debilis and Sergia filictum, have low maximum critical flicker fusion frequencies (CFFs) of 21-25 Hz, whereas the shallower living species Oplophorus gracilirostris and Janicella spinacauda have higher maximum CFFs (31-32 Hz). One of the shallowest living species, Funchalia villosa, has an unusually low maximum CFF (24 Hz), which may be a function of working with a dark-adapted eye. Two of the bilobed euphausiid species. Nematobrachion flexipes and N. sexspinosus, have very high maximum CFFs (44-57 Hz), comparable to those of surface-dwelling crabs, even though they live between 400 and 600 m. The maximum CFF of Stylocheiron maximum, a shallower living bilobed euphausiid, is only 36 Hz, indicating that maximum CFF among the euphausiids cannot be correlated with depth of occurrence. The unusually high flicker fusion frequency of the deeper living euphausiids may be correlated to their preference for bioluminescent prey.