RETINOMOTOR MOVEMENT OF ALL SPECTRAL CONE TYPES OF RED-SEA BREAM PAGRUS-MAJOR IN RESPONSE TO MONOCHROMATIC STIMULI AND UV SENSITIVITY

This paper examines the hypothesis that spectral cone types exhibit di fferent retinomotor movements in response to monochromatic radiation a nd can thus be identified histologically in the retina. Red sea bream Pagrus major, 79-105 mm in total length, were dark adapted in a glass aquarium, then exposed overhead to various intensities of white light and monochromatic stimuli with peaks at 337, 368, 466, 551 and 609 nm. The retinae from fish from each stimulus were examined histologically and scored for thickness of the cone layer and the pigment layer rela tive to the total retinal thickness. The red sea bream tested showed r etinomotor response to 368 nm but not to 337 nm, and therefore were co nsidered sensitive to ultraviolet stimulus. As additional single cones were absent in the cone mosaic, UV perception by central single cones or twin cones was suggested. White light and three other monochromati c, stimuli elicited the retinomotor movement of all single and twin co nes. These results and similar data from the literature show that the light-adaptive retinomotor movement of different spectral cone types i s triggered by light perception in rods and thus do not vary by wavele ngth of visual stimulus between 368 and 609 nm.