They Glow in the Dark

Studies have been carried out on 2 shark species, Chain catsharks and Swell sharks, that show bioluminescence (https://www.theguardian.com/environment/2019/aug/08/scientists-discover-why-two-shark-species-emit-green-glow). These fish live in the West Atlantic and the East Pacific at depths where only blue light can reach and on its exposure causes them to glow bright green. The bioluminescence is different from that seen in certain jellyfish (where it is used in medical diagnosis) and may be involved in mate-finding, as males and females have different light patterns. The skin-based chemicals may also play a role in defence against microbial infections.