The Victorians had a keen interest in nature. House plants were a novelty as were fish. A few rare examples of Victorian era fish tanks do exist. The one pictured is a reproduction of a Victorian tank based on illustrations from the era.
Other tanks look more like modern rectangular tanks. The cast iron rectangular tanks provide some ideas on how one might decorate a modern tank to make it more fitting to a room's decor. This large image of an antique tank has great detail to work from (click here for that image).