Eyes wide with wonder, Amy Hopperstad was already figuring out a design to combine her twin interests.

"I'm a gardener, and I like aquariums," Hopperstad said, scanning the aquaponics display at the California State Fair. "This is an awesome concept. I have an 80-gallon aquarium, and I was trying to decide what to do with it. I'm going to try this with koi."

Hopperstad, a Sacramento resident, had heard of aquaponics but had never seen a system up close.

She was mesmerized by the debut of aquaponics at the fair's greenhouse in The Farm, where steady streams of visitors are learning about the marriage of hydroponics and aquaculture to grow fish and vegetables in a closed, recirculating system.

The displays point to a growing enthusiasm statewide and locally in aquaponics, both as a backyard food source and as a business venture. Equipment companies are cropping up to serve hobbyists, schools are opening their doors to train aquaponic farmers, and advocates envision commercial operations to sell food at farmers markets, local restaurants and schools.

In an aquaponics system, water from a fish tank flows into a hydroponic grow bed. The water, rich with nutrients from fish waste, feeds plants growing in the bed. The plants' roots then act as a biofilter to purify the water, which is recirculated to the fish tank.

Advocates say the system grows healthier organic produce with up to 95 percent less water than conventional farming, which is significant as farmers struggle through the most widespread drought in a half-century. And the fish can be raised and sold in addition to the produce.

The systems can be set up in greenhouses in industrial settings and urban neighborhoods, eliminating the need for produce to make long trips to supermarket shelves, and creating business opportunities in vacant warehouses in cities across the nation.

David Rosenstein, western region chairman of the national Aquaponics Association, envisions aquaponics transforming food production in times of tight resources, global warming and the high price of oil. He said the technique yields six times the volume of produce and twice as many crop cycles as conventional farming.

Rosenstein said more young people are turning to growing their own food, and aquaponics could spark the economy and employment. Aquaponics is not only about environmentally sustainable farming, he said, but is a financially smart way to provide a safe and secure food supply.

"This is an emerging industry, and to be successful, we're going to need to train people," he said. "We need people to work, not just in farming, but in marketing and research, in IT skills, and many other fields. Not all of us in aquaponics will wear plaid shirts and straw hats. It's going to help if you have an MBA."

Rosenstein started one of California's first commercial aquaponic greenhouses, Evo Farms, in a greenhouse in a residential neighborhood in Los Angeles. He now grows up to 10,000 plants a year in a 500-square-foot greenhouse, including lettuce, Asian greens, peppers and tomatoes, which he sells at a local farmers market. He has experimented with using catfish, tilapia, carp, shrimp and crawdads.

He now has his sights set on a larger greenhouse that could provide food for a school district.

Rosenstein also designs and sells aquaponics systems that allow backyard gardeners to grow fish and produce in compact vertical towers. One of his kits is currently on display at the State Fair.

Paul Trudeau, Sacramento branch chairman of the newly formed state Aquaponics Association, is a pioneer in the local movement. He built a small system on his porch in 2010, stocked it with about 20 bluegills, and produced lettuce, peas and herbs for home use.

Trudeau helped create and maintain many of the displays at the fair.

"It's been a childhood fantasy of mine to grow fish that I could eat," Trudeau said. "We had fish aquariums as kids, and my brother was in the Peace Corps in Nepal, building and stocking fish ponds. I just always thought it would be great to be able to eat good food straight out of my backyard."

Aquaculture, raising fish for food, is seeing a spike in interest as a way to control quality in fish and to save wild fish populations. But the farming of fish often produces high levels of ammonia waste in tank water.

Hydroponic systems grow produce without soil, instead bathing the roots of plants with water. But growers have to add liquid chemical fertilizers.

When the two techniques are put together, Trudeau said, the fish waste provides the liquid fertilizer, while the plants cleanse the ammonia from the water and mitigate toxic levels of waste, creating a balanced ecosystem.

He started an online forum for Sacramento aquaponics enthusiasts, www.aquaponicscommunity.com.

"The Sacramento group is less than a year old, and more than 50 people have joined," Trudeau said. "It's a great catalyst for bringing people together and sharing information."

Trudeau said aquaponics in the Sacramento region is mostly for backyard hobbyists so far, but he can envision small greenhouse operations in the near future.

"A lot of people are experimenting with commercial applications," he said. "It hasn't happened here yet, but there are people interested in that. There's talk of systems getting started for farmers markets, restaurants and school districts."

Trudeau organized a tour of five backyard systems in June, which drew more than 40 people.

"It was really popular. In fact, we had to limit the number of people," he said. "We could have had double or three times the number."

The California Aquaculture Association is hosting the State Fair displays of aquaponics and partnering with the state aquaponics group to raise awareness of fish farming.

"Aquaponics is another way to grow fish and vegetables for consumption," said Tony Vaught, CAA president and a commercial fish farmer in Chico. "It's sustainable, clean, good for the environment and produces high-quality food.

"Having backyard fish farmers also will help aquaculture, as people connect personally to growing and harvesting fish. This helps our base in politics and regulatory issues."

Vaught said aquaponics can produce fresh, local food in areas of a city that are underused.

"This could be used in abandoned warehouses, and put people to work, especially those with physical limitations or veterans," he said.

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