It's actually a glass bowl. The white is marbling color with the blue/red that's at the tips of his fins. Other than the light reflecting off it, the glass is unmarked.
Reggie, your guy looks healthy floating there...I guess I'd have to take a video of Spike. He starts out straight, swimming up. He constantly has to correct himself but when he stops trying, he goes straight up and down and sinks. This pic was snapped in the process of going perpendicular and sinking.