Shining Sharks

Sharks glow in the dark. This may seem absurd, but recent research into the biofluorescence of fish has uncovered a startling new world of glowing fish. There are currently over 180 fish species that are biofluorescent. This means that the fish can absorb one wavelength of light, then reemit that light but at a lower energy wavelength (Sparks et al. 2014). The most common is absorbing blue light, which is the only type of light in most marine systems and emitting green light. They do this in order to be seen. Many fish, including sharks, have yellow filters in their eyes that would accentuate the biofluorescence of other fish(Sparks et al. 2014).

Park et al

Exactly how this happens in fish is mostly unknown. Only the chemistry behind eel fluorescence has been found until recently researchers unlocked how the swell shark and the chain catshark are able to glow (Park et al. 2019). Traditionally, green fluorescent proteins (GFPs) and other similar proteins have been found to enable bioluminescence, some of which have led to important innovations within the medical community (Park et al. 2019). But the researchers discovered a new type of protein, brominated tryptophan molecules, that enable these sharks to get their glow on. They discovered 8 new molecules in the sharks’ skin that are bioluminescent by using a battery of different methods to determine the shape and makeup of the different molecules, many of which are found more often in a chemistry lab than a biology lab (Park et al).

Park et al 2019

These molecules would seem to also play a dual role for the sharks. Not only do they fluoresce, but some of them actually have antibacterial properties (Park et al. 2019). This is especially important for the swell shark and catshark as they live on the seafloor, which has a much higher concentration of bacteria than the water above. Having these molecules in their skin may actually protect the shark from illnesses contracted from bacteria. There are other properties of these molecules that are unknown, and many other potential molecules in other fish that have yet to be discovered. These sharks and their amazing biology just may shed some light onto other avenues of exploration not just in the field of fish biology, but in fields such as chemistry and medicine.

Sources:

1. Park, H. B. et al. Bright Green Biofluorescence in Sharks Derives from Bromo-Kynurenine Metabolism. iScience 0, (2019).
2. Sparks, J. S. et al. The Covert World of Fish Biofluorescence: A Phylogenetically Widespread and Phenotypically Variable Phenomenon. PLOS ONE 9, e83259 (2014).