A comment was put up the site that was similar and got this response:
Quote:
You are correct that the light spectrum narrows greatly with increasing depths. We are investigating the evolution of colour vision from both angles and work is currently being undertaken to determine the molecular basis for the complement of cone pigments in a myriad of ray species. Interesting, some species of fish that dwell at even greater depths possess multiple cone types, suggesting that colour vision may be an important sensory system even when there is little light. Thus, the number and type of cones may not always correlate with the local light environment. In the case of cone monochromats, such as the wobbegong sharks and many marine mammals, the unanswered question is why they have a functional 'red' cone at all and not a rod-only retina?