Biofluorescent sharkskin suited and booted

Biofluorescent sharks and what other molecular and electricity of life implications? Chain catsharks and Swell sharks appear in blue light to have glowing scales.

Chain catsharks and swell sharks are deep-dwelling and live in the western Atlantic and eastern Pacific respectively, where they hide among rocks and rubble. While at first glance they appear to be in various shades of brown, recent studies have shown that under blue light they glow green. Crucially, only blue light penetrates the depths of the ocean...

Gruber and colleagues say a group of very different molecules is behind the green glow of the sharks, many of which have not been found before in natural settings... the team said the green glow of the sharks was limited to certain parts of their bodies – typically where the skin was paler or where there were white spots.
Scientists discover why two shark species emit green glow | The Guardian

The researchers describe a new form of biofluorescence as the headline and funding grabbing eye candy but they also interestingly suggest:

Bromo-tryptophan-kynurenines are biofluorescent and show antimicrobial activities. Specific dermal denticles in the chain catshark act as optical light-guides. This study opens questions related to biological function of shark fluorescence.
Bright Green Biofluorescence in Sharks Derives from Bromo-Kynurenine Metabolism

Biofluorescent sharks

Blue-green shark interface

We may need to look at sharks in a different light.

The team’s previous research has suggested the visual system of these sharks seems tuned in to such hues. They just have one visual pigment in their eye, said Prof Gruber. It sees right at the blue-green interface.

If these sharks are absorbing blue and then creating green [light], they are creating contrasts for each other, because there is no green [light] down there except the green that they are producing on their skin, he added.
Scientists discover why two shark species emit green glow | The Guardian

This shows that the green fluorescence is not only targeted to varying regions of the shark but also that the targeting is fine-tuned to specific denticle types within a shark species. It has been previously demonstrated that these shark species possess the visual apparatus to detect biofluorescence (484 and 488-nm monochromat visual pigments in C. ventriosum and S. retifer, respectively) and that there are pronounced sexually dimorphic fluorescent patterns. The green biofluorescence thus creates greater visual contrast for these sharks at depth, due to the primarily blue mesophotic marine environment.

It has also been shown that there are species-specific emission patterns in other fluorescent fish species, leading to the suggestion that biofluorescence functions in intraspecific communication and assists camouflage.
Bright Green Biofluorescence in Sharks Derives from Bromo-Kynurenine Metabolism

Sharks are even bacteria killing machines?

One of the most feared natural killing machines, they even seem designed to fight and kill dangerous bacteria.

The team tested the fluorescent substances for their action against certain bacteria: one found in marine environments and the other MRSA – the hospital superbug. Growth of both bacteria were found to be hampered by some of the substances within the sharks’ skin – a finding the team says might indicate that molecules involved in biofluorescence could also be part of microbial defence.

These sharks lay on the bottom and the bottom has a high density of bacteria, said Gruber, adding that substances in the skin might protect the animals. We are just hypothesising it could be a way to stop things from growing on the shark.
Scientists discover why two shark species emit green glow | The Guardian