On the upcoming podcast we explain amongst other things why the sea is blue and what happens to red light in water (subscribe to the rss to listen!). For depths over 10m red light is pretty much irrelevant to fish. There is no purpose to see it since it is largely absent, and therefore no value in displaying it. Or is there? Here is a paper in BMC ecology with some stunning pictures and an account of how actually not only are some fish red-fluorescent, but it is also a really good private communication solution:
"We here report that at least 32 reef fishes from 16 genera and 5 families show pronounced red fluorescence under natural, daytime conditions at depths where downwelling red light is virtually absent. Fluorescence was confirmed by extensive spectrometry in the laboratory. In most cases peak emission was around 600 nm and fluorescence was associated with guanine crystals, which thus far were known for their light reflecting properties only. Our data indicate that red fluorescence may function in a context of intraspecific communication. Fluorescence patterns were typically associated with the eyes or the head, varying substantially even between species of the same genus. Moreover red fluorescence was particularly strong in fins that are involved in intraspecific signalling. Finally, microspectrometry in one fluorescent goby, Eviota pellucida, showed a long-wave sensitivity that overlapped with its own red fluorescence, indicating that this species is capable of seeing its own fluorescence."
Not only is this cool in itself but it may be useful for us lab rats to use in imaging and microscopy as it would have different properties than RFP and current dyes.