xoxoxoBruce points to this gent,
http://www.fishighway.com, who has constructed an elaborate, well, fish highway between his two aquariums.
Yes there's water in it and yes the fish do swim through it! I can't imagine how heavy the whole thing must be - you'd want it anchored really well, because I doubt homeowner's insurance would cover the unique disaster that might happen... but in any case, it's a really unique and lively design project, very cool.
Anyone else have Habitrails as a kid?