Custom aquariums come in wide variety of shapes and sizes and can be a stunning way to bring some of nature's beauty to a room.

"Acrylic, and to a lesser extent glass, is very malleable, and any design you can conceive of that will hold water can be made [into an aquarium]," said John Holland of aquarium design company Blue Region in Silver Spring.

Holland has created tanks using everything from 150-gallon rectangles to an 8-foot-high, floor-to-ceiling cylinder. A big part of the process is creating a healthy environment for the fish. A high-end saltwater fish tank requires five or six operating systems, including ultraviolet sterilization, protein skimming and mechanical filtration. Freshwater tanks are simpler.

"Most people think that aquariums are just boxes of water, but in fact there's a lot more to it than that. They are basically living, breathing things," Holland said.

Blue Region:
Miche Booz:

With careful installation, the extensive machinery needed for a large aquarium can be placed where it will not detract from the aesthetic -- sometimes under the tank. But Holland recommends finding a remote location, such as a basement or garage. Maintenance for these tanks may require a professional service.

Before setting up the tank and equipment, homeowners need to choose between saltwater and freshwater fish.

"There's a continuing prejudice and myth that freshwater fish aren't are as colorful, when in fact there are quite a few species of freshwater fish that are fantastically colorful," Holland said, naming cichlids from Africa and Central America as an example.

Another popular option is a coral reef tank, which can be populated without affecting the endangered coral reefs along the U.S. coast.

Rather than buying corals taken from the wild and then bleached, there now are attractive artificial alternatives or living corals farmed in the ocean specifically for the aquarium trade. Some saltwater fish, such as the popular clownfish, now are captive-raised as well.

As a design element, architect Miche Booz, of Brookeville, Md., said aquariums can be used in either a sculptural or a functional way.

It simply can be a piece of art, "an object of curiosity and beauty that's interesting to look at," Booz said.

Another approach is to incorporate an aquarium into something that you already have.

For example, Booz designed a bathroom with an aquarium as part of a wall partitioning the room in two. He surrounded it with cabinets that both conceal the equipment and provide storage.

The aquarium's design must consider the well-being of the fish as well as the decor, one reason that Holland works with a minimum tank size of 150 gallons, generally starting at a cost of $15,000.

Holland said a smaller tank cannot maintain a stable enough environment, and he is as concerned about the animals as he is about aesthetics. "I measure success in fish that live for years," he said.