Theme Aquarium is a simulation where the player has to build and manage a sea life centre. This includes buying tanks, getting fish from suppliers, and training dolphins for shows. Players start with an empty floor they can decorate to turn it into a maritime wonderland. Revenue is generated by attracting visitors. They have to be able to see an interesting selection of creatures and their wishes are visible for the player to react. The player can catch fish and sea life, or buy it from a selection of sellers. The main attraction is usually the dolphin show. The animals need to be cared for and the player also has to hire staff to clean the centre and provide general maintenance. The gameplay is similar to Bullfrog's earlier titles Theme Park and Theme Hospital.