Duplex Retina in Seven Elasmobranch Species

Retinas of three lamnid and four carcharhinid sharks were examined under the light microscope. Rod and cone photoreceptors were found in the retinas of all seven species. Counts and measurements of both types of photoreceptors are presented along wIth rod:cone ratios for each species. These findings are compared with other recent retinal studies on elasmobranchs and it is concluded that the majority of elasmobranchs possess morphologically duplex retinas. Thus, the view that sharks have pure rod retinas must be abandoned. The general occurrence of duplex retinas in sharks is discussed in terms of visual physiology and evolution of elasmobranch visual cells.