Fish farming is a potential solution to the overharvesting of wild fish around the world. But there is a problem with some aquaculture businesses: Fish raised in cages in the ocean, or in tanks on land, often create high densities of waste.
An answer to this challenge, however, is now bubbling to the surface.
At a greenhouse in a Baltimore nature preserve called the Cylburn Arboretum, Dr. David Love, a Program Director at the Johns Hopkins Center for a Livable Future, is growing 500 fish. They are tilapia, a species of plant-eating freshwater fish that grow to about a foot in length, and they swim in four plastic tanks.
Pipes from these 250 gallon fish tanks send waste from the fish to a pair of pools, in which Styrofoam islands float. On these islands are plants growing without soil. The lettuce, spinach, eggplant and other vegetables thrive with their roots dangling into the water.
Dr. Love explains that the system is called “aquaponics.”
“Aquaponics is essentially a recirculating system where we are growing both fish and plants together, using the fish waste to fertilize the plants,” he said.
The word is a marriage of two other words: aquaculture; and hydroponics, the raising of land-based plants in water.
“Our approach to raising tilapia is taking the fish waste, and using it for something beneficial, instead of just saying ‘see ya!’” Dr. Love said. “We are claiming our waste, we are owning up to it, and we are doing something useful with it.”
There are also other critters involved in this symbiotic system.
Minnow-like fish called gambusia dart among the roots of the floating plants and gobble up the larvae of mosquitoes and other insects.
Between the tanks are plastic reservoirs swarming with millions of bacteria. These nitrobacter take ammonia in the fish waste that would otherwise be toxic and convert it into a form, called nitrate, that the plants can use as food.
Dr. Love said he has contributed some of his produce to a homeless shelter, and plans to sell his fish and vegetables in the future to urban farmers markets.
The project cost $15,000 and was funded by Johns Hopkins. Some critics of aquaponics have questioned question whether such farms will be profitable in the free market, when the cost of setting up and heating the greenhouses is accounted for.
One entrepreneur testing the financial viability of aquaponics is Ellen Perlman. She recently opened a company called Chesapeake Aquaponics in Reisterstown, Maryland. There she’s raising 200 tilapia and koy with floating islands of basil, kale and lettuce.
“I think it’s the wave of the future,” Perlman said. “This has a very high yield to the space. You can really grow in a small space of the rafts very luscious, beautiful vegetables, without using pesticides. And we are not using any pesticides or harmful chemicals.”
She hopes aquaponics will spread around the globe as a technique to create lots of food with little pollution and zero waste. But whether these floating gardens will also grow income may be the ultimate test of sustainability.
By Tom Pelton
Chesapeake Bay Foundation