Multiple rod layers increase the speed and sensitivity of vision in nocturnal reef fishes

Most vertebrates have one layer of the dim-light active rod photoreceptors. However, multiple rod layers, known as a multibank retina, can be found in over 100 species of fish, including several deep-sea species and one family of nocturnally active reef fish, the Holocentridae. Although seemingly associated with increased photon catch, the function of multibank retinas remained unknown. We used an integrative approach, combining histology, electrophysiology, and amino acid sequence analysis, applied to three species of nocturnal reef fishes, two holocentrids with a multibank retina (Neoniphon sammara and Myripristis violacea) and an apogonid with a single rod bank (Ostorhinchus compressus), to determine the sensory advantage of multiple rod layers. Our results showed that fish with multibank retinas have both faster vision and enhanced sensitivity to bright and dim light intensities. Faster vision was indicated by higher flicker fusion frequencies during temporal resolution electroretin...