Austria 2023 3 euro colour coin - Swell shark

The swell shark gets its name from its ability to inflate itself to roughly double its normal size by swallowing water as a form of protection from predators. When the shark feels threatened, it will bend its body into a U–shape, grab its tail fin with its mouth, and suck in water. Doing so causes the shark to enlarge in diameter and makes it much harder for predators to bite or dislodge. The swell shark is capable of swelling by using water or air, which is stored in the stomach until released. When letting air out, the swell shark makes a dog-like bark. But that’s not its only amazing property – the shark can also fluoresce green all over. Swell shark biofluorescence was first reported in 2014. To do so, the swell shark converts incoming ultraviolet light, or blue light, into green light. A special pigment in the sharks’ eyes enables it to see the neon green of its conspecifics. Human eyes do not have that pigment, which is why we need an ultraviolet torch to see the swell shark’s green glow. The molecules that make swell sharks fluoresce are unique in the animal world. The light areas of their skin glow more intensely than the dark ones. Why the shark does that is not yet fully understood, but it is assumed that the process helps swell sharks to recognise each other and to distinguish between the males and females of the species. It could also be a form of camouflage and because the molecules offer protection against bacteria and algae and just happen to glow. Swell sharks are non-aggressive and are considered harmless to humans.