Men, thats only a snippet of the original paper, the abstract i think. The original you can pay for in Nature magazine if anyone is really keen but i think that distills the main point. There is more info on the net. The same question came up a some years back on this forum and i remember reading one paper from a study in Hawaii which claimed capture of a hybrid giant and bluefin trevally!!
I still think the males have the ability to go from dark grey on top to really dark (black) when they are stressed, angry or in mating mode. In places like hawaii and the marquesas where the background structure is dominantly dark basalts; a silver fish in ambush would stick out like you know what; so perhaps in these localities the females also have the ability to pigment dark. This theory is just based on observation and a rudimentary understanding of fish biology though.
