Anatoly Konenko, a Russian artist who specializes in miniatures, holds a Guinness World Record for having built the smallest aquarium in the world. It's 30 mm wide and holds 10 ml:
The water has to be applied using a syringe so as not to disturb the landscape the Siberia-artist lovingly created.
Konenko, who calls his art 'micro-miniatures', even made a minuscule fishing net which he used to place the fish, baby Danios.
The adults are usually a favourite with more normal sized tanks but the tiny fish look at home in Konenko's construction for which he has since added a specially built air pump.
You can view several large photos and a video at the link.
Link via Make | Artist's Website