There are commercial applications to aquarium keeping. There are small businesses that attend to aquariums like for offices or residential setups. There are also aquarium makers, and carpenters that fashion the stands and other equipment. Marine biology comes to mind as well, perhaps in the aquarium keeping world in applications such as working for the large aquariums at zoos and other centers.
Then, though I am not sure, wildlife conservationists must try to keep endangered species in captivity to avoid them going extinct.