Reef fish get riled when intruders glow red

Male fairy wrasses get feisty when a rival fluoresces

1:58pm, May 29, 2014

RED MESSAGE  In the mostly blue world of a coral reef, a male fairy wrasse (left, illuminated with white light) will take note when one of its kind sports a fluorescent red glow (right, under blue light).

Even in the blue underwater realm, fish can see red in more ways than one. Reef fish that see glowing red patches on a rival aggressively bite and put on extra threatening displays, researchers say.

Red wavelengths from sunshine can’t penetrate water much deeper than 10 or 20 meters, failing to reach far into the realm where more than 40 small Cirrhilabrus fish species called fairy wrasses dart along reefs. But shorter, bluer wavelengths can plunge deep, where they are absorbed by the scales and some of the fin rays in both males and females of the C. solorensis fairy wrasse. The fish then fluoresce, emitting their own red light in distinctive his-and-hers swaths across their bodies.

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