Dr Tobias Gerlach, Dr Dennis Sprenger and Professor Nico Michiels from Tübingen's Institute of Evolution and Ecology made use of the fact that the male of the red-eye wrasse, Cirrhilabrus solorensis, reacts aggressively towards his own reflection in a mirror. In one experiment, a filter placed in front of the mirror blocked the fluorescent part of the fish's coloration -- with the result that males were far less interested in their mirror image. The researchers say this shows that the red-eye wrasse not only recognizes its species' special coloration -- it also uses it as a territorial marker and displays it in conflicts with other males.
One of the most exciting discoveries, the researchers say, is that the fluorescence is a deep red in a part of the spectrum which, it was previously believed, fish could not see or make use of. It could be that red-eye wrasses use their fluorescence as a private frequency to communicate amongst themselves.