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maxg
12-19-2001, 11:46 AM
I noticed a few posts about fish's vision at night. Well interestingly enough fish have rods for b/w and cones for colour, same as us, but the fish's rods are retracted and covered up in bright light. Takes some time to come up as the light is reduced. At night the vision is good, some fish like drums and the deep water fish, and sharks, have a tapetum, a reflective retina to increase b/w vision. Most pelagic fish seem blue/green since there is no red in the ocean and the low frequency colours, red/orange disappear at about 20 feet anyway, as do indigo and violet.
The ocean is a blue filter and the colour transmission changes as the particle content changes. Like as the water gets darker the colour filter shifts to green, then yellow then red, when the water is dirty.
There are a few papers on this subject, and some number of books, but you should look at Scientific American, Colour Vision in Fishes, about the 1986 era. Pretty good stuff.
But generally fish use the contrast of the fly against the pale water surface at night, there is always some light up there. But the only light in the ocean comes from above and light photons are still going to follow the same rules as in the atmosphere. White reflectsa all photons, black absorbs all photons and colours reflect their own photons. If fish do not see red, they do not see chartruse, but rather very bright green, but it appears to them, as a monochromatic thing, like white. Very bright white.
Max Garth.... In Australia, VBG.