Vision using multiple distinct rod opsins in deep-sea fishes
Vertebrate vision is accomplished through a set of light-sensitive photopigments, which are located in the photoreceptors of the retina and consist of a visual opsin protein bound to a chromophore. In dim-light, vertebrates generally rely upon a single rod opsin (RH1) for obtaining visual information. By inspecting 101 fish genomes, we found that three deep-sea teleost lineages have independently expanded their RH1 gene repertoires. Amongst these, the silver spinyfin (Diretmus argenteus Johnson 1863) stands out as having the highest number of visual opsins known for animals to date (2 cone and 38 rod opsins). Spinyfins simultaneously express up to 14 RH1s encoding for photopigments with different peak spectral sensitivities ({lambda}max=448-513 nm) that cover the range of the residual daylight, as well as the bioluminescence spectrum present in the deep-sea. Our findings present novel molecular and functional evidence for the recurrent evolution of multiple rod opsin-based vision in vertebrates.\n\nSHORT ABSTRACTContrary to the single rod opsin used by most vertebrates, some fishes use multiple rod opsins for vision in the dimly lit deep-sea.