Please DON'T mirror...that's the EASY way. You folks have worked hard on this wonderful screensaver that you should go ALL OUT and make both monitors as a SINGLE fish tank, with the fish swimming between monitors. Please don't mirror. Continued success to all involved!
What you ask for would require twice as much coral, in other words twice the effort or a whole other month piecing together photographs of coral and finding the right combination, then building the 3D lightplay objects.
Jim Sachs' current focus is the Freshwater Aquarium. Beyond that, he will be replacing the flat background we have now with a truly 3D double-width background with real moving coral elements including clams that open and close, and anemones and polyps that sway with the ebb and flow of the water.
This double-width background will be ideal for dual monitors, widescreen displays and regular displays. Depending on the aspect ratio of your display, the background will slowly pan back and forth to reveal the part that is off-screen.
I think supporting widescreen and dual monitors and giving us lifelike coral is great, but I think spending a month right now developing another piece of flat coral (which would be thrown away in favor of the 3D coral) would be counterproductive.
I think we'll see mirrored display on multiple monitors until the 3D background arrives.