A luminous animal kingdom

Some sharks, like this cat shark, glow green in the dark. New York biology professor David Gruber successfully found the molecule which causes the shark to glow. The "brominated tryptophan-kynurenine" metabolites might also be responsible for warding off bacterial infections. In contrast to other animals, such as jellyfish, the fluorescent substance is not a protein, just a component of it.

For humans to be able to witness — and cameras to be able to capture — fluorescent animals under water, black light is used. Gruber’s colleague Jason Crawford is fascinated by sharks. "We really don't have a firm grasp on shark biology. And they're just incredibly amazing creatures with all kinds of fascinating superpowers," researcher Jason Crawford said.

These small Pterophyllum Scalare — commonly known as angelfish — have been genetically engineered to glow. Not all glowing fish have been created by humans, though. Nature has many other examples of luminous animals.

The jellyfish begins to glow when mechanically stimulated, for example, by water turbulence. Experts describe bioluminescence as the ability to produce light by oneself or with the help of bacteria. There are over 180 identified species of bioluminescent fish.

Even protozoa are able to produce light, like this dinoflagellate, a member of the sea plankton family. Deformities in their cell membrane, caused by breaking waves or fast swimming fish, enable their light to glow. With that, this unicellular organism is able to confuse predators.

The most common example of a glowing animal is the firefly. They produce luciferin, which reacts with oxygen, and then generates light. Males and female fireflies communicate with each other via light signals.

A lot of deep-sea fish have the ability to illuminate themselves — including this hatchet fish. Some inhabitants of deep ocean produce light in order to orientate themselves better where there is no light. Others use it to attract prey.

Even photostomias from the barbeled dragonfish family have the ability to shine. The deep-sea fish lights up an organ behind its eyes which emits red light – an unusual color for marine organisms. Other sea dwellers cannot see this species’ light signal.

Mice don’t usually glow. But, things can change in a laboratory. Researchers manipulated the rodents so they produce green fluorescent protein in their cells. This protein occurs naturally in some jellyfish species. Under a blue light, the mouse glows green – but, not their fur.

Theoretically, genetic engineering can make all animals glow. A research institute in Uruguay created these lambs, which glow yellow when placed under a UV light.