A closed ecosystem produces tomatoes and fish in northern Sweden
By growing fish and tomatoes in the same ecosystem, the fish produce fertilizer for the tomatoes and the tomato plants clean the water for the fish. With this system, 1 kilo of fish food produces 1 kilo of fish and 10 to 12 kilo if tomatoes. The video is in Swedish but you can see some of the facilities.
Best regards, Niklas 🎈
It is crazy how beautifully balanced nature can be.
All the best, Leia
Host of Gluten-Free Living | News | English Language 
What a great system.
Happy creating!
Tammie
Host of Paints and Crafts
What do the fish eat?
My website: American version
Min hemsida: Svensk version
Some kind of fish food. You can read about it at www.peckas.se.
Best regards, Niklas 🎈
A similar type of technology has also been implemented in some places in the UK if I remember correctly. They use the same techniques on rooftops so that you can farm in a sustainable manner in urban centres.