Aquariums can be categorized using several different systems. A common distinction is between community aquariums, species aquariums, and ecotype aquariums. We can also divide aquariums into three broad groups depending on their salinity: freshwater aquariums, brackish aquariums and saltwater aquariums (marine aquariums). Each category can then be further subdivided into many smaller categories. A saltwater aquarium can, for instance, be a fish-only aquarium (FO), fish-only with live rock (FOWLR) or a reef aquarium. An ecotype aquarium can be classified according to its biotope, e.g. a Malawi aquarium, a Tanganyika aquarium or a Southeast Asian Blackwater Pool.
The most common type of aquarium for beginner aquarists is a tropical freshwater community aquarium. In a community aquarium, you can mix many different fish species as long as they are not aggressive or consider each other prey. You can also include suitable plants from all parts of the world. When you select fish for your community aquarium it is important to select species that are non-aggressive and appreciate roughly the same temperature and water quality. Experienced aquarists sometimes keep aggressive fish species in a type of community aquarium. Even though several species from different parts of the world live together in the same tank, these aquariums are usually referred to as “aggressive tanks” rather than community tanks.
An ecotype aquarium will not mix fishes, plants and other aquatic creatures from different parts of the world. An ecotype is instead designed to mimic an existing ecosystem. You can for instance set up a Malawi shore aquarium by using only fish that inhabits the rocky shores of Lake Malawi. Rocks should naturally be used as an aquarium decoration, and you should try to create plenty of caves and crevices – just like in Lake Malawi. A good thing about the biotope aquarium is that you can know for sure that all organisms will appreciate the same water quality. When you set up a Central American Fast-Moving Stream aquarium and use only plants, fish and invertebrates that are native to a Central American fast moving stream you know that they will require the same water temperature, water hardiness, pH etcetera. Many aquarists are also attracted to the idea of creating a quite well functioning eco-system within the ecotype aquarium. Public aquariums will often be huge ecotype aquariums since this gives the visitor a better understanding of the true habitats.
A species aquarium is an aquarium that houses only one fish species. A species aquarium can be home to anything from one single fish to a huge school; the important thing is that all the fish will belong to the same species. Some species will need a planted aquarium to do well, while others will eat or uproot plants. There are also many species that can do well in a planted as well as an unplanted aquarium. Species aquariums are sometimes set up as breeding aquariums since normally peaceful fishes can turn territorial and aggressive during the spawning period and must be removed from the community aquarium. Separating breeding fish from other adult fish is also a way of ensuring a higher survival rate for the offspring.