Hmmm... very interesting article, however I am not sure that I am convinced that this implies that fish can "see" red light from a red light source. For example, imagine someone gave you a similar test with two colored discs, one which was green (hence it reflects only light in the wavelength of green light) and hypothetically something that only reflected in the UV. We could distinguish between them because the one that reflected in the UV would look black. However it is not that we can "see" the UV disc for its reflecting of UV light but rather that it reflects no light we can perceive and therefore looks black. Therefore this would not imply that we could see UV light coming from a UV. Actually this is a horrible example because many things tend to flouresce in UV light and therefore output visible light when exposed to UV therefore a room illuminated by pure UV light would seem to glow. But anyways you get the point. Had the fish been forced to choose between a black disc and a red disc I don't know that would have been able to distinguish between the two.
