Abstract: A new toilet tank assembly aquarium for housing aquatic creatures. The assembly includes a toilet bowl assembly with a toilet tank assembly coupled to the toilet bowl assembly. The toilet tank assembly has a top, a front, a back, and a pair of sides. The front, back and sides of the toilet tank assembly define an interior space with the top of the toilet tank assembly having an opening into the interior space of the toilet tank assembly. A toilet water reservoir is located in the interior space. A lid substantially covers the opening of the top of the toilet tank assembly. The front of the toilet tank assembly is generally transparent.