Abstract
The aquarium is based on stable vertical temperature gradients. Different sections, where temperatures can be regulated by the incoming water, are separated by partitions allowing free passage of fish between each section. Seepage of water between the sections is prevented by varying the water levels of the different sections through the outflow system. The temperature distribution in the aquarium is monitored. Testing of the stability of the system was made by adding ink to the water supply of one of the sections. The utility of the system was demonstrated on the three-spined stickleback, Gasterosteus aculeatus L.