Curr. Biol. doi:10.1016/j.cub.2009.12.047 (2010)

Some fish are thought to communicate using covert signals: ultraviolet (UV) coloration that is invisible to their predators. The idea is supported by the finding that Ambon damselfish (Pomacentrus amboinensis, pictured, top) can differentiate between their own species and the near-identical lemon damselfish (P. moluccensis, pictured, bottom) using tiny differences in UV facial patterning.

Credit: U. SIEBECK/ELSEVIER

Ulrike Siebeck at the University of Queensland in Brisbane, Australia, and her colleagues found that, in general, territorial P. amboinensis attacked members of their own species more than they did P. moluccensis, but that this correlation broke down when the potential rivals were presented to one another in UV-opaque tubes.

The authors went on to show that trained fish could differentiate between species using images of facial patterns (pictured, right) that reflected either UV or visible light.