Aquaponics: Fish and Garden at the Same Time
by JD Hortwort
Do you remember, as a child, growing a sweet potato vine from a tuber, carefully suspended in a glass jar? The spud was delicately dangled about halfway in water, held up by toothpicks poked horizontally in its sides. You probably didn’t realize you were experimenting with hydroponics.
Perhaps you tried your hand at raising goldfish or brightly colored neon tetras as your first pets. If so, you were dabbling in aquaculture.
If you combine these two concepts, you have a bright new idea—aquaponics. According to Peg Godwin at the North Carolina Cooperative Extension, “aquaponics is defined as a food production system using the recycling of fish wastes to provide nutrients to support plant growth. The system has two products: fish and plants.” You might be old enough to remember a novelty gift from the 1980s—a decorative large glass vase with a Siamese fighting fish circling in the water. A peace lily (Spathiphyllum) was the plant of choice suspended overhead, held in a mesh basket at the top of the vase, roots dangling in the water. This is a very small example of an aquaponics system.
The History
Actually, calling aquaponics “new” is a bit deceptive. It’s a new concept in the modern agricultural community, but it’s not new to the world. Land-based aquaponics systems were known to Central American natives and Asian cultures that used systems of canals fed by nearby rivers to irrigate their various crops. If you’re letting water in from a river or stream, it’s bound to have fish in it.
The waste produced by the fish nourished the surrounding crops. As for the folks who worked the fields, did they eat the fish that were wiggling around their legs? Of course they did! They might not have bragged about their skills in aquaponics, but they had a hearty dinner each night. When efforts were made to move these farming practices from canals to self-contained water systems, aquaculture and hydroponics parted ways for a while.
The concept of controlled hydroponics is a bit more modern. It first emerged in the 1930s as researchers began growing plants in water, gravel, rock wool, perlite or some other loose material (anything but soil) while supplementing with nutrients via drip irrigation or frequent drenches.
Enterprising farmers and researchers combined the two ideas in the 1980s and aquaponics was born.
In Practice
My first encounter with this intriguing idea was when I learned about a young man in my area who wanted to get into growing crabs commercially. As a business reporter for a local newspaper located four hours from the coast, I must say I was curious and maybe just a bit amused.
But as the young entrepreneur explained his plan to me, I was amazed. A recently discharged military serviceman, he had come home with a Southeast Asian bride. As they shared their cultures, he learned that her family farmed a special type of crab in the Indonesian islands. I believe it was the black or mud crab, Scylla serrata.
This crab grows quickly to an extraordinary size, larger than North American crabs. Not only is this crab content to live in a contained aquaculture system, it is said to be very tolerant of high nitrate and ammonia levels in the water.
According to my young businessman, it reaches a mature, marketable size in roughly six months, a fraction of the time it takes an Atlantic crab to get to the same size. Foodies were just beginning to discover its delicate flavors, he said. At the time I was working on the article, the meat could sell for upwards of twenty dollars per pound.
Obviously, he couldn’t grow South Sea crabs outdoors in Piedmont North Carolina. This businessman had found a vacant warehouse. He intended to set up commercial tanks inside with climate controls. He had the aquaculture part of this down pat.
To generate money while the crabs were growing, he planned to grow salad greens for area restaurants. These would float in special trays in the crab ponds. Most salad greens come to maturity in six weeks. With coordinated schedules, he expected to harvest crabs at least three times a year and salad greens pretty much continuously all year long.
Aquaponics is a self-sustaining form of agriculture that combines plant and fish cultivation. As of 2018, the largest commercial aquaponics operation in the US was in Northfield, WI, where operators expect to harvest 30,000 heads of lettuce daily and 160,000 pounds of fish annually.
Sadly, his backing fell through before his dream came to fruition. That doesn’t mean the idea isn’t very doable, even if you only want to produce fish and plants for your immediate family.
How It Works
I once heard a joke in which one person asked where the superhero Aquaman went to the bathroom. Fortunately, the conversation took a turn before the discussion got too graphic. But it does raise an important point central to aquaponics.
Fish, like all animals, have to relieve themselves in the very water they swim in. Why don’t they die in a toxic sludge?
According to researchers, fish can survive due to the volume of water and a complex relationship between them, plants, and the beneficial bacteria in the water. This relationship works even in standing water, such as in ponds or enclosed bay areas. A simple explanation of what happens goes like this:
A key component of all animal waste is ammonia. Land animals excrete this in urine in ways I’m sure everyone is familiar with. Fish excrete ammonia through their gills. Once in the water, bacteria eventually turn ammonia into nitrates. Plants use nitrates. In a balanced, natural setting, the nitrates are mostly used up by plants on stream banks or pond shores or by plants living in the water. When everything is in balance, this is a perfect setup.
When it gets out of hand, we see algae bloom and overgrowth on the banks at water’s edge. You have probably seen a farm pond covered over with a green coat of algae and scum. But let’s not dwell on the negative. When the system works, fish produce a by-product that can be used by plants and we, as humans, can be the beneficiaries.
Do It Yourself
Aquaponic systems come in all shapes and sizes. My entrepreneurial friend was interested in building long troughs that would have plant trays floating on top while his crabs matured in recirculated water below. That’s why he wanted to rehabilitate an old warehouse that had plenty of light and plenty of space.
Some large systems maintain the fish in a separate container and pump the water through nearby stacks of plant trays. For a time, our local community college taught aquaponic classes that used large tubs, roughly forty inches tall and about eight feet across. I discovered this while working on a different business article. In this setup, the plants removed the nitrates they needed for growth. The water was filtered to remove any impurities that might harm the fish. It was then sent back into the fish container.
Obviously, this can be done on a large enough scale to become a half- or full-time business or just large enough to keep a family stocked in produce and fresh fish.
However, there is a simple way for a homeowner to benefit from aquaponics, and it doesn’t entail a huge vat of fish. It involves a ten-gallon fish tank, a soil-less growing medium, a plant tray, and small produce sets or seeds. In this case, you’ll be enlisting the fish as laborers to provide most of the nutrients your plants will need to grow. I suppose you could eat the fish, but they probably wouldn’t even make a mouthful after cleaning and gutting them. Better to head to your local sushi restaurant if you have a hankering for raw fish.
To develop this project, I started with the instructions from an industry journal and modified them to fit my goals.
The first task is to set up your fish tank.
For the fish tank:
10-gallon tank
Enough fish tank gravel to create a 2–3-inch thick layer at the bottom of the tank
Water pump that moves roughly 75 gallons of water per hour. This is a little larger than what you would need if you were just sitting up a fish tank because it has to pump water up and into the plant bed.
4 feet of plastic tubing that will fit onto your water pump
Small fish (no more than 10)
Set the fish tank up according to the instructions. Wash the gravel before putting it into the tank. Nothing says you can’t also put any decorative items into the fish tank, like plastic plants or little underwater castles. It won’t interfere with the production of produce, and the fish might like the diversion.
Fill the tank with water. My father was an amateur fish hobbyist with a 20-gallon tank. He always advised letting the water set for 24 hours before adding fish.
Attach the plastic tubing to the water pump and nestle it into the bottom of the tank. One source recommends using an air pump to aerate the water, but most of my sources didn’t. Whenever my father set up his tank, sometimes he used an air pump; sometimes he didn’t. I opted to go without.
Now it’s time to take care of your plants.
For the plants:
Plant tray
Soilless medium like perlite or vermiculite. I’ve tried growing plants in pea gravel but I find it too heavy.
Plants grown in a soilless mix. You can purchase plants grown in soil, but you will need to wash the soil away, thoroughly cleaning the roots, and reset the plant in your soilless mixture.
The plant tray should be a couple of inches wider than your fish tank and just a little shorter in length. It will balance on top of the tank. It should be at least 6 inches deep. To be safe, wash it thoroughly before you begin.
Before adding the growing medium, measure 3 inches in from each side of the tray. Drill multiple holes with a 1/8 bit into the bottom of the tray. The bottom should look like a colander with a solid 3-inch border all around. This will allow water to drain back into the fish tank without running outside the tank. On one end of the tray, measure up at least 3 inches from the bottom and drill a hole big enough to accommodate the plastic tube you attached to the fish tank water pump.
Thread the tube into the plant tray. The tube should loop like a long U shape, running to the end of the plant tray and back up to where it starts. If the tube is too long, cut it back to fit. Bend the end of the tube over and use a small alligator clip or strong rubber band to keep it crimped. Notice where the tube comes into the tray. Beginning about 10 inches from that point, carefully make a hole in the tube about every 2 inches. This is how the water will be feed into the plant tray. The water will flow back into the fish tank through the holes you drilled in the bottom of the tray.
Set the plant tray on top of the tank and fill with the soilless mix. Run your system for a day to make sure nothing leaks. Then you can add the fish and plant your tray. The number of plants will depend on the type of plant. Lettuce plants can grow closely together, spaced about 2 inches apart. Herbs will need more space, approximately 4 inches apart.
Monitor the system daily. Over time, you will need to add water because the plants will take up some. Harvest will take a little time, but you should be ready for your first salad in about 4–6 weeks!
Plant and Fish Varieties
What kind of plants can you grow in an aquaponic garden? Just about any kind you can imagine. For this fish tank aquaponics project, it’s best to stick to small produce like lettuce, spinach, and other greens. For herbs, try chives, basil, parsley, dill, and savory. From my experience, it’s best to stay away from herbs that like especially well-drained, low-humidity conditions like rosemary, sage, or ground cover thymes.
The fish you grow can be varied as well. I prefer goldfish, but koi are perfect for this project. You can also use zebra fish, guppies, or my father’s favorite, neon tetras—really any freshwater fish you find at your local pet store will thrive in an aquaponics system.
Common Pitfalls
As with any gardening project, I have to caution people not to assume this is a hands-off endeavor.
You have to monitor the system. This means testing the water periodically to manage the pH levels and to control for possible bacterial infections. If you purchase plant sets from a nursery, it is still possible to accidentally contaminate your system.
Filters need cleaning and changing from time to time. This is especially critical in small systems like our fish tank. Periodically, you will need to break down and clean the system, doing so with gentle cleaners that won’t harm the fish.
Your plants will get the necessary nutrients from fish waste but you still have to feed to fish! This should be done daily.
A small, ten-gallon aquaponic fish tank is usually set up indoors in a home or classroom, so climate control probably isn’t a problem, especially for the fish. What will become a problem is light quality. Even salad greens need sufficient light to grow in the winter or in low-light conditions. You may find it necessary to add a plant light over your indoor garden.
Disease and insect control on the plants shouldn’t be a problem either. However, should that come up, treat plants early with an organic control approved for use around fish. For example, a mild soap insecticide will take care of aphids with little danger of harm to the fish. A control like neem oil is safe for plants but could be harmful to the fish, so read labels before you apply anything.
Aquaponics Supplies and Resources
You can buy most of the items for a small fish tank aquaponics project at any garden center or big box department store. Farm supply stores can be another beneficial resource.
In North Carolina, our cooperative extension service has put a lot of resource material out there for small and large aquaponics operations. These can be accessed at ces.ncsu.edu. Or you can explore what is available at your own extension office by going to outreach.usda.gov/USDALocalOffices.htm and clicking on “USDA Cooperative Extension System Offices.”
Finally, as with most industries, there is an association for that. In this case, you will find information at the Aquaponics Association website aquaponicsassociation.org. This can lead you to other state and regional organizations.
Aquaponics can be a fun project for students or for those like the elderly who can’t get out to garden as much as they might like. For the rest of us, not only is aquaponics a self-sustaining form of agriculture, it’s a great way to extend the growing season throughout the year.
Selected Resources
Bradley, Kirsten. “Aquaponics: A Brief History,” Milkwood (blog), January 20, 2014. https://www.milkwood.net/2014/01/20/aquaponics-a-brief-history/.
Nelson, Rebecca. “Build a Mini Aquaponic System.” Nelson Pade. Accessed September 17, 2018. https://aquaponics.com/build-a-mini-aquaponic-system/.
Sawyer, Tawnya. “Aquaponics: Growing Fish and Plants Together.” Colorado Aquaponics. Accessed March 15, 2019. Slideshow, 72 slides. https://www.scribd.com/document/351734340/Tawnya-Aquaponics-Intro#fullscreen&from_embed.