Tropical Fish And Aquarium Rentals business. Business Overview Gigantic profits can be earned by starting a tropical fish and aquarium rental business, and best of all, this very unique enterprise can be set in motion for less than $5,000 and managed right from a homebased office. At this point, I am sure you're wondering exactly who would rent tropical fish and an aquarium? The list is very long, and if you think about waiting rooms, the list of potential clients can include...