Yesterday a small group of us went for an excursion to Basel to join a presentation of the Aquaponics project of Urban Farmers - quite interesting approach to grow fish and tomatoes (and other plants) at the same time, nourishing each other. So it can be considered a valuable extension of the Hydroponics system introduced by Pepy below.

The Urban Farmers' aquaponics project is quite focussed on "efficiency" though (I pitied the fish which are living in large groups of 100-200 fish in plastic tanks), but in the end it's a business model developped from a research project, and they seem to be quite successful, selling to restaurants and a well-known Swiss supermarket.

Here is more about the Aquaponics project (in English): http://urbanfarmers.com/technology/aquaponics/