The rich world of the luminous fish

"Until now, we knew that marine creatures such as corals and jellyfish, and even terrestrial animals such as butterflies and parrots, are capable of glowing. But the existence of a parallel phenomenon in fish has been reported in few studies", says John Sparks, curator in the fish department at the "American Museum of Natural History"

A team of international researchers led by scientists from the "American Museum of Natural History" and with the participation of Dr. Dan Chernov from the Department of Marine Biology at the University of Haifa published the first report on the distribution of natural luminescence (Biofluorescence) in the fish tree of life. Researchers have identified over 180 species of fish that have the ability to glow in a wide variety of colors and patterns.

The term Biofluorescence describes a phenomenon in which organisms absorb light, process it and emit it as a different color. In the study, which was published on January 9, 2014 in the journal PLoS ONE, the researchers claim that the phenomenon of biofluorescence is a fairly common phenomenon that varies between different fish species. This fact indicates a potential for use in communication and mating. The first report opens the door to the discovery of new fluorescent proteins, which can be used in biotechnological research.

"Until now, we knew that marine creatures such as corals and jellyfish, and even terrestrial animals such as butterflies and parrots, are capable of glowing. But the existence of a parallel phenomenon in fish has been reported in few studies", says John Sparks, curator in the fish department at the "American Museum of Natural History" and a leading researcher in the study. He adds that "this article is the first to examine the wide distribution of the biofluorescence phenomenon among fish, and opens up several new areas of research."

In contrast to the full rainbow of colors that characterizes the world of man and terrestrial animals, fish live in a world that is mostly blue, because as we go deeper into the seabed, most of the light spectrum visible to our eyes is absorbed. The research team discovered that many fish absorb the remaining blue light and re-emit it in fluorescent green, red and orange colors.

David Gruber, professor of biology at "Baruch College" and a research fellow at the "American Museum of Natural History" explains that "by combining a lighting system that imitates the light of the ocean with cameras capable of capturing the neon light emitted by the fish, we can for the first time glimpse into the universe This hidden bio-fluorescence". Many of the inhabitants of the shallow reefs have the ability to detect fluorescent light and it is possible that they use biofluorescence to find mates and camouflage, in a manner similar to the use of bioluminescence (emission of light by a living organism as a result of a chemical reaction) by certain animals.

The research began by chance, with the discovery of a green eel glowing with fluorescent light, while Grover was photographing glowing corals in the Cayman Islands, for the exhibition "Creatures of Light: The Biological Illumination of Nature".
Sparks, Grover and other researchers from the John Pierce Laboratory at Yale University, the University of Kansas and the University of Haifa, joined a group of professional still and video photographers, and went on four expeditions in the Bahamas and the Solomon Islands. During night dives, the researchers "stimulated" the biofluorescence ability of the fish using blue light arrays in boxes designed for lighting in the water. The result was an underwater light show invisible to the human eye. In order to record the activity of the fish, the researchers used special underwater cameras that contained yellow filters to block the blue light. At the same time they used yellow headlamps which allowed them to see the glow of the biological lighting, while swimming over the reef.

The last observation was made in the Solomon Islands, under the auspices of the museum's new management, which supported multidisciplinary field work and the integration of new technologies. From the research ship "Alucia" the researchers carried out dives in diving suits as well as trips in submarines containing three people, with the aim of studying the biological lighting of coral reefs at a depth of up to a thousand meters. Their scientific research was submitted for publication while on the ship.

The four expeditions discovered a zoo of luminous fish: from cartilaginous fish such as sharks to gram-like fish such as eels and lizard fish. Through photographs, collecting samples from the sea water and conducting additional studies in public aquariums after hours, the researchers discovered over 180 species of luminous fish, including entire families. Some use their ability to shine for camouflage and are difficult to locate.

According to the researchers, many luminous fish have yellow filters in their eyes, and these allow them to see the neon displays in the water. Although more research is needed, this significant finding indicates that biofluorescence lighting can be used as a means of internal communication between the fish of the same species, while maintaining camouflage from predators.

"Flatfish, eels and scorpionfish are types of fish that we will never notice while diving," notes Sparks. "To the human eye, these fish blend in with their surroundings; But in the eyes of a fish with a yellow intraocular filter, the luminous fish stand out like a bone in the throat."

In addition to this, the researchers discovered that the biological lighting ability varies greatly from species to species, starting from the eye rings, through a glowing green secretion on the skin of the fish, and ending with complex glowing patterns all along the body, and even inside it. This difference indicates that the ability to glow evolved several times in fish in separate evolutionary paths. Future studies on the mechanisms of the phenomenon may reveal new illuminating proteins, which will be used in experimental biology. In this context, Gruber notes that "the discovery of a green fluorescent protein in a hydrozoan jellyfish during the sixties provided a revolutionary tool for modern biologists and significantly changed scientific research, starting with studies on the AIDS virus and ending with studies on the functioning of our brains." He further adds that the discovery of biofluorescence in fish can be another rich source for the discovery of new fluorescent proteins.

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