It's not so rare to have in an aquarium the birth of a Siamese fish but it's almost impossible that they could reach the adulthood. That's why these images are so incredible.
Two conjoined Nile Tilapia fish, dubbed "Siamese Twin", swimming in a small aquarium in Bangkok. They are both eight months old and share part of the skin together. The bigger fish tends to protect the smaller one from harm while the smaller one looks for food at the bottom of the aquarium.