Like all creatures on this great big wonderful world, fish come in a huge variety of species from several different geographical regions. The variations in geographical origin makes the difference in fish size, color, eating habits and life expectancy as well as the vigor of the immune system. Most aquarium fish available and popular today originated in Central America, South America, Africa, or Asia. Fish can be kept in different combinations of species and in different kinds of aquatic environments and their are five common themes in the world of aquariums:

1. The community aquarium
2. The goldfish aquarium
3. The African cichlid aquarium
4. The planted aquarium.
5. The Biotope aquarium.

1. The community aquarium is in reference to the mixing of fish and plants from different geographical areas with an emphasis on the color and hardiness of all specimens as a community. An example of a community tank would be one which contained a combination of gouramis, tetras, and rasboras with a selection of hardy plants such as Hygrophila difformis, Hygrophila polysperma, and Vallisneria spiralis. One of the key ingredients in setting up a community aquarium is choosing fish that are peaceful and compatible with each other to ensure a harmonious existence.

2. The goldfish aquarium is probably the most well-known and basic aquarium installations often small, between 3 and 20 gallons, set up as minimally-furnished or bare-bottom tank to keep things as simple and maintenance free as possible and to emphasize the bright coloration of the fish. Using  combinations of different species of goldfish and decorations that contrast with the vivid colors of the fish. Live plants can be used but are not usually grown with goldfish, except for hardy, oxygenating plants like Egeria, because goldfish regularly disturb the substrate.

3. The African cichlid aquarium commonly consists of cichlid varieties like the Lake Tanganyika cichlid or Lake Malawi cichlid. These are usually larger size and generally do best with a large number of rocks combined with a fine gravel or sand substrate. The rocky environment provides numerous caves and hiding places for the fish and provide a more interesting habitat so the fish don't become complacent or bored with a uniform and stagnant environment with no challenges, twists or turns to keep things fun. Because cichlids, like goldfish, disturb the substrate by digging, plastic plants should be used as a substitute for live plants. However, real plants like Vallisneria or Anubias can be tried in a cichlid tank.

4. The planted aquarium places more emphasis on the living plants as much as, or even more than the fish. Abundant groupings of dramatic plant species such as Hygrophila, Limnophila, Rotala, Vallisneria, Echinodorus, and Cryptocorynes are introduced into a receptacle with a limited number of fish. This is a good example of a planted tank. It is important to select fish that will not damage the plants or if they do the damage does not effect the health of the system. Fish such as small tetras, dwarf gouramis, cherry barbs, zebra danios, and White Clouds can cause issues so population guidelines should be adhered too. Planted tanks often include CO2 injection and a substrate fortified with laterite or, in the case of a low tech aquarium, a layer of potting soil under the gravel to provide nutrients for the plants.

5. A biotope aquarium is an aquarium that is designed to simulate a totally natural habitat, with the fish, plants, and furnishings all representative of a particular place in nature. Because only species that are found together in nature are allowed in a true biotope aquarium, these tanks are more challenging and less common than the other themes of aquariums..