Seahorses don’t fluoresce well, but the algae that covered the spikes on this one’s back gave off a very strong red fluorescence that made it look as if the seahorse were on fire.

Raimundo Fernandez

Hard corals and anemones fluoresce better than almost any fish you’ll find, but this devil scorpionfish in Indonesia — extremely colorful and patterned even in daylight — gave off remarkable oranges, greens and reds.

Ethan Daniels

An underwater collage of corals with an anemone in the center, taken with blue-light photography, showcases the green and orange fluorescence of the creatures at night. Some researchers theorize that anemones use fluorescence to attract prey.

Barry Brown

Some of the most fluorescent animals are anemones and corals, like this long polyp leather coral. The dynamic behavior of the long polyps waving as they open and close gets an even cooler dimension under the ultraviolet light.

Raimundo Fernandez

The fluorescence of this orangutan crab (Achaeus japonicus) taken in Dauin, Philippines, accentuates the red fine hairs of its tiny body, measuring at roughly 2 centimeters.

Alex Tyrrell

Scientists do not know why certain corals — like this mushroom coral — fluoresce, but it’s theorized that the phenomenon might protect shallow-water corals from coral bleaching and help deeper-water species with photosynthesis.

Alex Tyrrell

The complex vision system of the mantis shrimp permits it to detect colors people can’t see, including ultraviolet light. It’s believed that the crustaceans use fluorescence as a “here I am” signal during mating rituals or as a warning when threatened. By using a filter, photographers are able to capture what other mantis shrimp see when one of its brethren lights up.

Alex Tyrrell

The dramatic lighting and open-mouth of this green moray eel make for a perfect find in the shadows.

Ethan Daniels

Coral reefs are the greatest place to enjoy fluorescence, but even in sandy beaches by night you can find some fluorescence subjects like this sand lizard fish (Sinodus saurus). A closer crop creates a completely different view.

Raimundo Fernandez