Fig. 3. Sleep swimming in the damselfish Dascyllus marginatus measured by video filming them in infrared light on a coral reef in Eilat, Red Sea. The stroke frequencies of the dorsal, pectoral and caudal fins are about doubled at night when the fish hide inside coral (Stylophora pistillata) compared to the `normal swimming' performed outside the coral during the day. From Goldshmid et al. (Goldshmid et al., 2004). Reproduced with permission from Limnology and Oceanography.