I checked this book out at the library awhile back. While it has some good information on light penetration and the way light appears underwater, I would take the parts on how fish perceive color with a very hefty grain of salt.
You have to remember that fish are a very diverse group of animals. What goes for one group doesn't necessarily mean all animals in the same class see the same way. Take mammals, for example. Most mammals can only see a very limited range of colors compared to humans. Old world primates are generally considered to have color vision similar to humans, but new world primates have vision similar to other mammals except in a few species where only the females have color vision similar to ours. Some mammals that lack our range of color vision can see ultraviolet light that is hidden to us.
Trout can also see reflected UV light, which is different than UV fluorescence. Blacklights do not show reflected UV, only fluorescence. It's possible for a material to reflect UV and not fluoresce. For example human skin is not UV fluorescent, but here's a UV reflective photo of someone's face:
The only way humans can see reflected UV light is with sophisticated camera filters, and even then it's no guarantee fish see the same results.
