Fish tanks can be any size or shape. Everything from the common most common 10 gallon size, all the way up to whatever size your room will support.
They include marine aquariums, and freshwater aquariums. These can be placed on a piece of furniture, in the corner of any room in the house. Or they can be wall mounted. Were they actually inserted into a wall.
Probably the most used is a 10 gallon. Aquariums usually are glass or acrylic. Both of these types of tanks have their pros and cons. Glass can be broken or cracked and care must be taken to prevent this. Plexiglas is more durable, but they are sooner to scratching, obscuring the view of the fish.
Aquariums come in about any size. The most common shape is a rectangle. Round fish tanks are common also. In my opinion both the round and octagon tanks, distort the view.
Freshwater tanks are much easier to clean, than saltwater ones. Whereas a freshwater tank can be kept healthy and vibrant with very little work. In contrast a saltwater tank needs to have daily attention.
To balance out the extra work of a saltwater aquarium, salt water fish, are more exotic and have more vibrant colors.
Some of the easiest to take care of are Gold Fish and Beta fish tanks. Beta fish are also known as Siamese fighting fish. These fish tanks take the least amount of maintenance of all. Last of all there is a virtual fish tank . Instead of being in the room, they are actually a screen saver on your computer.