So.. this shot from last year is my good friend Lily La Mer (http://www.lilyshowgirl.com) She's a circus performer, model and professional mermaid.
This photo was taken in a tank just marginally wider than the space Lily was taking up, with numerous lights outside the tank. It was the first time I'd walked into a difficult lighting situation with little idea of what to expect and worked my way through the setup to create something we were all pleased with.
Reflections from the tank meant that there could be no frontal lights at all, not even fill.
An additional complication was the impossibility of communicating with the model, and the random chance element that moving in water brings.
It then took a fair amount of post work to remove the tank frame and scratches on the glass.