An aquarium was an artificial environment for aquatic life.
During an attack from a temporal mine, the TARDIS shared its pain with the Tenth Doctor by vaporising the aquarium which caused him to feel the dead fish in his gall bladder. Christina hoped that the Doctor would get his aquarium back. (PROSE: Keeping up with the Joneses) Later, the Eleventh Doctor searched for the aquarium but gave up on finding it after opening the doors to several other rooms. (PROSE: Shroud of Sorrow)