Researchers identify previously unknown mechanism through which sharks produce eerie glow

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Scyliorhinus canicula
Small-spotted catshark, Scyliorhinus canicula (Credits - Wikimedia Commons)

Unlike other creature, glowing catsharks that are present in the saline depths have a fluorescence mechanism that could be conferring some serious perks – such as the ability to pick out other sharks among the many fluorescent things on the seafloor

Biologist David Gruber of the City University of New York said that after they first reported that swell sharks were bio fluorescent, he along with his collaborators decided to plunge deeper into the topic learning more about bio fluorescence and its meaning which is constantly evolving mystery. The study has been published in iScience.

Evolution is a funny thing. Animals that are very different from one another can end up doing the same cool tricks. This phenomenon is called parallel evolution, and it can be fascinating to observe.

Biofluorescence, as an example, is a phenomenon in which living organisms like frogs, scorpions, chameleons, turtles, and a whole plethora of sea creatures can absorb and re-emit light in a different colour which is not to be confused with bioluminescence in which organisms glow with the light they produce themselves.

Majority of animals fluoresce by producing a green fluorescent protein (GFP), proteins that are very similar to GFP, or fatty acid-binding proteins (FABP). But the biofluorescent glow produced by a different chemical pathway is seen only in the two species of catshark – The Chain Catshark (Scyliorhinus retifer) and the Swell Shark (Cephaloscyllium ventriosum) both of which are flecked with light and dark patterns.

The sharks’ glow is produced by brominated tryptophan-kynurenine small-molecule metabolites, found only in the lighter parts of patterned skin while it is involved in the immune system and the central nervous system in other vertebrates. The metabolites in the shark’s skin help produce fluorescence in low-light conditions on the seafloor.

This is invisible to the human eye but the sharks’ eyes can see it, that’s why fluorescence wasn’t discovered until 2014. They channel that fluorescence through their scales, or denticles specifically structured for the task, so that they gleam with the re-emitted green light.

Researchers think that as it’s a different chemical pathway from those used by other sea animals, it might be a secret visual language which only shark understand. Chemical biologist Jason Crawford of Yale University said that because of these biofluorescent characteristics that their skin shows and that their eyes can detect, they have a completely different view of the world and to see each other which no other animal can link to.

Researchers want to determine the role of metabolites in keeping the sharks clean. Both the species of catshark spend a lot of time in the sediment, which contains more bacteria than the water column and having anti-fouling properties. Staphylococcus aureus and Vibrio parahaemolyticus, the two bacterial pathogens when pitted against isolated metabolites, two of the metabolites showed some ability to inhibit the growth of these bacteria showing antimicrobial properties.

Gruber said that sharks have been fascinating creatures for over 400 million years and the study highlights yet another mystery of sharks and inspires us to learn more about their secrets and work to better protect them.

Journal Reference: iScience

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