There are sharks that live in the depths of the sea that are capable of emitting a bright green light that only other sharks are capable of seeing. This is the case of the cat shark and the malleus allitan.
This fluorescence is different from that used by other marine animals and fulfills very specific functions such as helping to identify each other and fight against microbial infections.
The mechanism that allows this fluorescence has been published in the journal iScience and is due to an unknown family of small metabolites found in these types of sharks .
This type of biofluorescence that is only visible to other sharks was discovered by observing that these two species of sharks had two skin tones, one darker and one lighter.
Biofluorescence in sharks
Moved by curiosity and the knowledge that these sharks are biofluorescent, they analyzed the two areas of the skin, looking for chemical substances that would explain it. Thus they discovered that fluorescent substances are only found in areas of lighter skin .
When they analyzed these metabolites, they discovered that they discovered an entirely new form of biofluorescence in sharks based on brominated small molecules of tryptophan-kynurenine.
These small metabolites were known to be fluorescent and to activate metabolic pathways similar to those that in other vertebrates play a role in the central nervous system and the immune system.
In sharks, these variants of fluorescent molecules influence the biophysical and spectral properties of fair skin. This mechanism is different from animals that live on the ocean surface like jellyfish and corals that normally use fluorescent green proteins as mechanisms to transform blue light into other colors.
The funny thing about this system is that they can see each other fluorescent but are not visible by other animals. As one of the authors says, “imagine if we were bright green but only you could see me bright green, while others could not.”
It is especially interesting that these biofluorescent molecules show antimicrobial properties . These cat sharks live on the ocean floor, yet we don’t see any biofouling or growth on top of their skin, which could help explain another surprising feature of shark skin.
Knowing the bioluminescence systems in animals not only allows us to know the ecology, but it is also useful to design and develop new imaging techniques for diagnosis or research.