The Fish Tank is a furniture you can build (the Indoors page).
In-game description
A tank of desert glass of clear water for five fish you've caught, one to a place. Watch them swim. E to open it.SHOWN IN THE BUILD RING
Building it
It costs 4 
Wood, 4 
Stone, 1 
Pearl, 2 
Glass, 3 Water 2 Earth spirits. It needs 1 Jewel first. Take it down with DISMANTLE to get its cost back (see Building).
