Many models are taken from http://www.3dchaya.com.
The plant in the lower right corner is taken from http://www.3dplants.com,
while the kois are taken from http://toucan.web.infoseek.co.jp/3DCG/3ds/FishModelsE.html.
All remaining parts (like bridge, floor or fish tank) were created by ourselfes or by procedural functions we designed (like mountains in the fish tank and outside the window).

We used Blender to design the scene.