This seems like it would be to small for even a single neon tetra (and cruel little person inside of me wants one)
http://www.thinkgeek.com/computing/usb-gadgets/e5dd/?cpg=145H&head
I did the math and the tank is 5.7"x3.5"x4.7" or 0.4 Gallons
http://www.thinkgeek.com/computing/usb-gadgets/e5dd/?cpg=145H&head
I did the math and the tank is 5.7"x3.5"x4.7" or 0.4 Gallons