Scientists have determined that red fluorescence in reef fish helps with their vision and not always UV protection as previously thought.
Red fluorescence eyes of reef fish at deeper depths may be used as a visual aid.
In a paper published in the Proceedings of the Royal Society B, researchers used a procedure called fluorometry to measure the amount of red fluorescence brightness in eight common small reef fish species with red fluorescent eyes. What they found was that the red fluorescence was much brighter in fish residing on parts of the reef that are less than 20 meters in depth than those living on the reef at less than 5 meters in depth in six of the eight species of fish. They found no difference in the remaining two species of fish.
The study looks at two views with regard to red fluorescence in the eyes of reef fish:
1) That shallow water reef fish with red fluorescence in their eyes gives the fish photoprotection in waters where UV is strongest, and 2) that red fluorescence at deeper levels greater than 10 meters enhance visual contrast, enabling fish at these depths to have greater visual clarity. At these depths, the red in the 600-700 nanometer range has already been absorbed.
The scientists measured the amount of red fluorescence around the eyes of several species of fish from the family Gobiidae, Syngnathidae, and Tripterygiidae.
Tthe majority of deeper water fish collected for the study exhibited brighter red fluorescence than those fish collected at shallow depths. The scientists believe that red fluorescence is used as a visual aid and not always to protect against UV. They still believe that there may be some protective elements in red fluorescence in the eyes of reef fish, especially at the shallower depths.
The scientists speculate that the red fluorescence light emissions may be used to detect prey. The fish in the study included those from the family Gobiidae, including the redeye goby (Bryaninops natans), spotted pygmy goby (Eviota guttata), pygmy goby (Eviota zebrina), Michel’s ghost goby (Pleurosicya micheli) and a sand goby, (Fusigobius cf. duospilus); one fish from the family Syngnathidae, the black-breasted pipefish (Corythoichthys nigripectus); and from the family Tripterygiidae, the black-faced blenny, (Tripterygion delaisi) and triplefin blenny, (Helcogramma striata).
The complete paper can be found on the Proceedings of the Royal Society B website here.