The "Frit plexiglass" idea stems out of a concept I once saw for a skyscraper which looked like it was disappearing into the clouds. The architect intended to use stainless steel mesh at the top part, of less density at the tip. It had a good fade away effect, much like that of Frit glass, but without reflection issues.
Maybe your tail could be translucent by use of thin unpainted fiberglass.
I did not mean for you to copy the Dolphin in any way, think beyond that concrete example.
Below is the closest image I could find with a light skin effect, ugly as sin, but you should get the idea.
Architects float prison-in-the-sky idea | Crave - CNET
