LONDON: Over 180 species of fishes have been identified that glow in a wide range of colours and patterns in the world's oceans.
These include both cartilaginous (sharks and rays) and bony (eels and lizardfishes) lineages — especially among cryptically patterned, well-camouflaged species living in coral reefs.
Scientists from the American Museum of Natural History have released the first report of widespread biofluorescence in the tree of life of fishes.
biofluorescence — a phenomenon by which organisms absorb light, transform it, and eject it as a different colour — is common and variable among marine fish species, indicating its potential use in communication and mating. The report opens the door for the discovery of new fluorescent proteins that could be used in biomedical research.
Unlike the full-colour environment that humans and other terrestrial animals inhabit, fishes live in a world that is predominantly blue because, with depth, water quickly absorbs the majority of the visible light spectrum. In recent years, the research team has discovered that many fishes absorb the remaining blue light and re-emit it in neon greens, reds, and oranges.
"By designing scientific lighting that mimics the ocean's light along with cameras that can capture the animals' fluorescent light, we can now catch a glimpse of this hidden biofluorescent universe," said author David Gruber. "Many shallow reef inhabitants and fish have the capabilities to detect fluorescent light and may be using biofluorescence in similar fashions to how animals use bioluminescence, such as to find mates and to camouflage"
"We've long known about biofluorescence underwater in organisms like corals, jellyfish, and even in land animals like butterflies and parrots, but fish biofluorescence has been reported in only a few research publications," said John Sparks, a curator in the museum's department of ichthyology. "This paper is the first to look at the wide distribution of biofluorescence across fishes, and it opens up a number of new research areas".
During night dives, the team stimulated biofluorescence in the fish with high-intensity blue light arrays housed in watertight cases. The resulting underwater light show is invisible to the human eye. To record this activity, the researchers used custom-built underwater cameras with yellow filters, which block out the blue light, as well as yellow head visors that allow them to see the biofluorescent glow while swimming on the reef.
The team also noted that many biofluorescent fishes have yellow filters in their eyes, possibly allowing them to see the otherwise hidden fluorescent displays taking place in the water. Although more research is needed, this finding indicates that biofluorescence could be used for interspecific communication while remaining camouflaged to predators. This ability might be especially important during full moons, when fishes have been shown to partake in mating rituals.
"The cryptically patterned gobies, flatfishes, eels, and scorpion fishes — these are animals that you'd never normally see during a dive. To our eyes, they blend right into their environment. But to a fish that has a yellow intraocular filter, they must stick out like a sore thumb," the team said.
Source: Times of India , January 12, 2014