Who says that growing food has to mean polluting the air and water with pesticides and herbicides? Certainly not Tom Hopkins (PhD '68), a leading proponent of aquaponics.
Imagine, for a moment, a farm on which fish are raised in tanks, vegetables are grown in water or soilless engineered medium, and nothing is wasted. That's right, nothing. The water the fish are raised in recirculates, and their wastes fertilize the hydroponic crops. The concept is known as "total resource recovery," and it's one for which biologist Tom Hopkins, president of Maryland's Aquaculture Association, is an ardent spokesman.
"Although there are a host of possible refinements, the basic principles are the same as you'd use in a home aquarium," Hopkins explains. "Keep good water circulating and exposed to air so that the fish have enough dissolved oxygen to breathe--remember the trickling sound you hear from a tropical fish tank? Then, feed them and do something with the wastes they produce."
At present, food growing is a net environmental loss, Hopkins points out. Irreplaceable topsoil is washed away; by- products are wasted or become pollutants themselves; herbicides and pesticides pollute the air and water. These threats to the environment will only become more acute as the world's population burgeons (the United Nations predicts a jump from 5.4 billion in 1990 to 7.2 billion in 2010), and the needs for food increase.
Hopkins is convinced that one solution to these environmental threats lies in aquaponics--a process that marries aquaculture (fish farming) with hydroponics (growing vegetables in water). By giving more emphasis to aqua- ponics, he believes food growing could actually become a net gain to the environment.
Aquaculture is not new to the United States. "Trout hatcheries go back to the late 1800s, when states and private concerns started them to stock their streams and promote recreational fishing, both for residents and visiting vacationers," explains the 54-year-old Hopkins. It is to these hatcheries that fishing enthusiasts today are indebted for the wide spread of brown, speckled, and rainbow trout (indigenous only to the Pacific Northwest), as well as small- mouthed, large-mouthed, and striped bass--not to mention the salmon now found in the Great Lakes.
Commercial aquaculture began to spread throughout the United States around 1985, when the limits of the world's natural fish populations had become glaringly obvious. Today, we find catfish in Mississippi and cultured crawfish in Louisiana, trout growing in Idaho, and succulent (and expensive) abalone in California. Salmon grow in floating pens in saltwater bays of Maine and Washington, while in Washington state, cultivation of an oyster species native to Japan is now claimed to provide the bulk of oysters consumed in the United States. Other entrepreneurs will probably emulate these successes, and hybrid bass and tilapia are on the rise--especially tilapia, a tropical fish increasingly seen in supermarkets, which breeds easily and is less picky about either food or water quality. Neither fish was found at seafood counters 10 years ago.
Tom Hopkins's introduction to the field began far earlier than the mid-'80s, during the energy crisis of 1973. "I intuitively felt the oil energy crisis would lead to problems with water and food," he recalls. A year later he left the National Institutes of Health, where he had been working as a research scientist, to launch a small farm of conventionally grown vegetables near Boyds, Maryland. After reading articles about the success of recirculating systems, he says, "it occurred to me to try to link up vegetable growing and fish farming." Today he grows between 10,000 and 20,000 fingerlings (young fish) each year, as well as a variety of aquaponic vegetables.
Over the years, his farming efforts have become one of many sidelines. Hopkins also builds and sells aquaculture and aquaponics equipment, and he develops strains of bacteria beneficial to fish farmers and wastewater treatment. Most of his energies, however, are devoted to his consulting company, Biometrics, which serves aquaculture enterprises around the country. He's become known among growers as a water quality specialist. When the fish mysteriously go belly up, Hopkins is the man to call.
"Recently someone called who grows ornamental and food fish. He was worried because they weren't swimming right, eating right," Hopkins recounts. "I'm familiar with his operation and water conditions, and I thought I knew what the problem was as soon as I got there: carbon dioxide." In testing the pH levels of the water in which the fish were waiting to be shipped, he found one case with a level of 5.6, another with 6.2. In water that acidic, carbon dioxide becomes toxic to fish. "But this is something most growers don't have the equipment to test for. They don't even think about it," he says. "Carbon dioxide isn't even listed on the EPA's checklist for water criteria. But after we buffered the water, everything was fine." On other occasions the biologist has been asked to grapple with environmental regulations, as in the case of Hunting Creek Fisheries of Thurmont, where he helped the company improve the quality of its discharge water to meet new state standards.
Ideally, of course, he'd like to see aquafarms in which there is no discharge of water, or at least very little. Which brings us back to his enthusiasm for total resource recovery.
To show how it works in practice, he points to Bioshelters, Inc., a company that cultivates tilapia and edible plants in one continuous, integrated system in a greenhouse in Amherst, Massachusetts. In 1993 Bioshelters produced 30,000 pounds of tilapia, as well as 4,000 cases of hydroponic produce that was grown in the same water as the fish. Bioshelters's founder and president is John Reid, who as a college student spent the summer of 1983 interning with Hopkins. "He set me on the path to total resource recovery," says Reid. Today Hopkins continues to serve as a frequent advisor.
Bioshelters's basic premise is that all the food put into the fish tank--ALL of it--becomes either fish or plant tissue. No used water is flushed down a sewer or into a river, where it can set off algae blooms and suffocate fish. Here's how the system works:
As the tilapia swim about in Bioshelters's greenhouse ponds, they expel ammonia through their gills, which becomes ammonium upon hitting the water. This ammonium is consumed by naturally occurring benign bacteria, which leave behind a nitrite solution. (These nitrifying bacteria are given a sand filter on which to attach.) Then another set of bacteria attacks the nitrites, creating nitrates.
Nitrates are the prize, because they are absorbable by plant roots. In fact, as any gardener knows, nitrogen is a key plant food listed on commercially sold fertilizers. Reid gets the sought-after fertilizer for free, simply by circulating the fish waters through tubes that feed his hydroponic greenhouse crops--basil, wheat grass, and some lettuces.
Bioshelters even makes use of the fish feces, which can pose a problem for aquafarms because they eventually build up and may harbor pathogens that make the fish sick. Reid culls out the waste and pumps it to a nearby marsh. After several months of bacterial action the waste turns to sludge and is then spray irrigated onto adjacent vegetable fields, where a farmer raises more than 10 varieties of specialty crops, mostly high-value vegetables.
No pesticides are used in the Bioshelters greenhouse. Instead, Reid maintains a guest population of beneficial bugs. The "good bugs" are content to stay in their own little "eco-island"--a section of the greenhouse loaded with their favorite foods--until a crop is invaded by insect pests. Then the hired bugs swoop in to eat the bonanza of invaders.
One key benefit of this recirculating system is that it conserves water. Reid needs to replace just 0.3 percent by flow--3 to 5 percent of the volume each day.
Reid points out that adding fish to a hydroponic vegetable system makes it more profitable. "An integrated fish-and-vegetable grower can earn quite a good income compared to a small conventional farmer," he says. "It's also helpful to grow high-value plants near a high-income area, or have enough people nearby who value the organic, better quality of your product and are willing to pay for it."
Both Reid and Hopkins believe that hydroponic-type fish- and-vegetable systems could work well in the growing urban areas of Southeast Asia--Thailand, Indonesia, and Bangladesh--where residents already are familiar with growing fish in neighborhood tanks. Agronomist Norman MacLeod, who has worked for nearly 30 years in Africa and Asia, shares their enthusiasm. "The initial set-up of the system is complicated, and experts would be needed for that, but after that a system like the one Tom promotes is pretty much, biologically, a perpetual motion machine."
Even in areas where a recirculating system is not possible, says Hopkins, the value of soils can be improved by applying fish feces. Fields could be irrigated with waste fish water by using raised ponds and manually operating valves, he says. No known freshwater fish diseases are transferable to humans, so there is no fear of contaminated crops.
"Just from the small amount of digested feces that stay in our water at Bioshelters, we have 20 or 30 mineral salts--things that gardeners refer to as trace elements," says Reid. These minerals, like magnesium, potassium, calcium, copper, and zinc, are all essential for long-term productivity of the soils, says agronomist MacLeod. "Rich, organic soils bring about robust plants that can fight off disease and pests."
Across the country, there are signs that the benefits of resource recovery are catching on, Hopkins says. Consider:
Linda Weimer writes from Pocomoke City, Maryland. Her articles on aquaculture have appeared in The New York Times and Maryland Magazine.
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