Aquarium

An aquarium is the name given to a tank of water that is designed to hold species which require an aquatic environment.

Prior to 2265, Hikaru Sulu and his grandfather once visited an aquarium which contained a shark. It was then that his grandfather told him to "observe the wisdom of the shark, Hikaru. It knows that if it stops swimming, it stops breathing.  So it continues to swim". 

In the 2260s the sickbay aboard the USS Enterprise (NCC-1701) was equipped with an aquarium. In 2270, Captain James T. Kirk and Spock were held in it after a forced mutation had restructured their lungs to work under water. 

Montgomery Scott created an aquarium aboard the stolen Klingon bird-of-prey HMS when the ship traveled back in time to 1986 in order to transfer humpback whales George and Gracie to the 23rd century. 

In the 2360s, Captain Jean-Luc Picard kept his pet lion fish, Livingston, in a small spherical aquarium in his ready room aboard the USS Enterprise (NCC-1701-D). ( et al.)