Scientists discovered that certain fish are capable of glowing red. Due to absorption of red wavelengths of sunlight by seawater, objects which look red under normal conditions appear grey or black at depths below 10 metres. This has contributed to the belief among marine biologists that red colours are of no importance to ocean fish. The authors identified at least 32 reef fish species belonging to 16 genera in five families that fluoresced visibly in red. The authors speculate that red fluorescence may function as a communication or attraction signal, as proposed for other fluorescent animals.