UV coloration

If you look closely to the brown trout, you will noticed they have a small blue patch just behind their eyes, on the gill plate. Those blue coloration could be very shinny at times. They should have some UV reflection, as the blue coloration always get into the UV section. The UV-blue color are fascinating, more and more literature "discover" this new color are very important for animal communication! The main reason it become a hot topic now is because 1) we "human beings" do not see UV...2) (stay tuned)