The Jumping Fish Theme has got to be one of the more surreal mobile skins I've seen. In fact, if Salvador Dali had a Windows Mobile device, I'm sure this would be the first thing he installed.
The principal image in Jumping Fish Theme features a plucky goldfish leaping out of the water. The wallpaper also features some weird egg-type objects and lots of squares with crosses on them floating about. Quite what all this means is anyone's guess.
The Jumping Fish Theme also alters the appearance of some of the other elements within the WM interface. A deep, royal blue color with gradient is added to the top and bottom menu bars, and a new Start menu design is applied, which actually makes the options very readable.
I'm not too sure why you would choose to install the Jumping Fish Theme, but I get it's quite appealing if you like surrealism.