I thought I might enter this discussion to clear up a few issues regarding ultraviolet light.
The near ultraviolet (wavelengths from 320nm to 400nm, a.k.a., UVA) can penetrate water up to 600 meters deep. The reason divers wear fluorescent patches is because the UV causes the patches to fluoresce, long past the depth of visible light.
Phosphorescence is the ability of a material to emit light over a period of time. Fluorescence is when photons of light (usually UV wavelengths) are shifted to a longer wavelength and immediately emitted - usually as a visible light.
Diffuse reflection (as compared to shiny, mirror-like specular reflection) of UV light is how many animals identify each other. For example, all tested families of birds see in the UV (as well as RGB). Typically, male birds will have "honesty markings" which are only visible in the UV. As the bird ages, the honesty markings fade and the female knows that, although identical in visible light to a younger bird, this one is an old fart and not worth her time -- even if he buys the drinks. :)
Here is an example of GP crest in visible light. They appear identical -
and the same thing in reflected UV
notice how much brighter the crest on the left is than the other in the UV?
Regarding whether trout see in the UV. They lose most, but not all of the UV specific cones during the smolt stage. However, all of their cones have a secondary peak in the UV, so as the percentage of UV increases at dusk, the UV vision begins to predominate. At night, the rods of the retina are used and these are actually more sensitive to UV than to visible light.
Why worry about it? One reason is that mayflies use UV vision at night to identify their mates by species and gender using UV specific markings. When you only have one night of love, it seems worthwhile to spend it with the right species. :) Trout are going to see these markings. If your Adams has them, but your buddy's doesn't, who will be likely to get a confident rise?
Just some thoughts.