Secret weapon red light

At a depth of roughly ten meters the colorfulness as we know it at the ground ends. The water filters yellow-, orange- and red tones almost completely out of the sun light. The underwater world becomes a slate blue monotony. In this colorless surrounding some fish developed tricks how they can yet generate red light independently. They use it profitably for hunting and when it comes to the choice of a partner. That is what researchers of the Eberhard Karls University Tübingen in the journal Frontiers and Evolution (4, 126, 2016) report. “The animals have fluorescent color cells that receive blue ambient light that they then in turn emit as red light, Professor Nico Michiels, head of the survey, explains.

Predators such as scorpions or flatfish, researchers assume, secrete red light to be camouflaged more effectively beneath likewise red fluorescent seaweeds while hunting. “So they stand out less while lurking for their prey” Dr. Nils Anthes says, leading author of the study. Plankton eating gobies emit red light especially around the eyes. Researchers assume that this serves a so far unknown mechanism comparable with the echolocation of bats. In doing so red light hits the eyes of small animals in the plankton and illuminates them. With this the animals reveal their position and become an easy prey for the gobies.

And finally, those who have red light at hand in big sea depths have a clear advantage when it comes to the choice of partner. The researchers think that by red fluorescence, signals are strengthens or newly generated that are preferred by selective females and display an especially good genetically condition of the male.

Red light looms large under water, much bigger than previously assumed, the researchers say. “It seems that fish developed during their evolution a full bag of tricks to extend their within their environment clearly reduced color palette on their own”, Nils Anthes says.