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Fish + Food = Science of Aquaponics *

Difficulty
Time Required Very Long (1+ months)
Prerequisites Read the following Science Buddies resource on Measuring Plant Growth
Material Availability Readily available
Cost Very High (over $150)
Safety Use caution when using drills and power tools. Be sure to wear safety goggles. Adult supervision is required.
*Note: This is an abbreviated Project Idea, without notes to start your background research, a specific list of materials, or a procedure for how to do the experiment. You can identify abbreviated Project Ideas by the asterisk at the end of the title. If you want a Project Idea with full instructions, please pick one without an asterisk.

Abstract

Watching fish swim around a tank is not only a soothing activity, but (along with learning how to care for the aquarium inhabitants) it is also a good introduction to ichthyology, the study of fish. But having pet fish doesn't have to be a passive hobby; you can put those fish to work by helping to grow food for you and your family. How? By designing and building an aquaponics system.

Aquaponics combines hydroponics with aquaculture. Hydroponics is the science of growing plants without soil in nutrient-rich water. The nutrients are exactly tailored to nourish and meet the growth requirements of the plants. Plants need nitrogen, phosphorus, potassium, and a variety of micronutrients to thrive. Normally, in a hydroponics system, synthetic fertilizers added to the water provide all of these essential nutrients. Aquaculture is the breeding and farming of aquatic organisms, such as fish, crustaceans, and aquatic plants, usually for human consumption.

In an aquaponics system, the fish provide nutrients in the form of their "waste," or excrement. This waste contains nitrogen in the form of ammonia (too much of which can be toxic to fish), along with a variety of nutrients like phosphorus and potassium. Nitrifying bacteria that live in the gravel in the fish tank and on the tank walls convert the ammonia first into nitrites and then to nitrates. The water in the tank, which contains ammonia, nitrites, nitrates, phosphorus, potassium, and other micronutrients, is continuously pumped into a grow bed where the plants are located. The plants remove the nutrients from this water, and nitrifying bacteria in the grow bed (working together with the tank filter) clean the water by converting excess ammonia into nitrates, which plants use to grow. The clean water is then sent back into the fish tank. The grow bed and plants act as a biofilter, cleansing the water so that the fish remain healthy. In smaller, backyard aquaponics systems, the grow bed sits on top of the fish tank and the cleansed water from the grow bed drips back into the tank. In aquaponics, the fish, plants, and beneficial bacteria all depend on each other to live. Watch this video to learn more about commercial aquaponics.

Aquaponics video 00:04.
Watch this video
which discusses commercial aquaponics and the advantages of aquaponics.

What are some advantages of growing food in an aquaponics system? First, it is efficient, producing from one system both food with high protein content (fish) and food with vitamins and minerals (vegetables). Second, aquaponics is mostly a closed system regarding water consumption, because it uses recirculating water. This means it uses minimal water and can be set up in arid areas that don't have plentiful water. All that is required is food for the fish. Finally, aquaponics is a model for sustainable food production because it integrates hydroponics and aquaculture, meaning that it recycles all of the materials it uses. This is good for our environment because instead of feces-filled water being dumped into our water system and causing problems downstream, it is used to grow plants, is subsequently cleaned, and then recirculated through the fish tanks.

There are three primary methods for growing food aquaponically: the raft method, the nutrient film technique (or NFT), and the media-filled bed method. The raft method grows plants on boards (rafts) in tanks separate from the fish tank, where the raft supports the plants and the roots of the plants sit directly in the water. Water flows constantly from the fish tank, through filters, through the rafts, and then back to the fish tank. This method is used commercially, as shown in the video above, and the extra volume of water in the raft tank is a benefit as it provides a buffer for the fish so they are not stressed by possible water quality problems. With the nutrient film technique, instead of growing the plants in tanks with their roots submerged in the water, the NFT trickles a thin film of water over the roots of the plants, which are grown in narrow channels. This method is not used as heavily as the other two methods because it requires a biofilter to provide additional nitrifying bacteria. In the media-filled bed method, the plants grow in a box filled with a growth medium, such as perlite or gravel, on top of the fish tank. Water from the fish tank is pumped into the box and then percolates through the growth medium and back down into the fish tank. The kinds of plants that can be grown depend on the density of fish in the tank. Lettuce and herbs require low to medium nutrient levels, so they don't need a high density of fish, while fruiting plants like tomatoes have higher nutrient requirements and therefore need a higher density of fish to supply their nutrient needs.

In this environmental engineering science project you will design and build an aquaponics system using fish from your local pet store, like goldfish. Since this project deals with nonhuman vertebrate animals your science fair may require SRC approval. Review Science Buddies' Scientific Review Committee (SRC) page for additional tips. Read the first reference in the bibliography to learn one way (the media-filled bed method) to build an experimental system. Use the aquaponics system to grow lettuce and basil and compare their growth to plants grown conventionally in soil. Compare the area of the leaves and the root systems between the two methods. Is there a color difference between the roots? Do the roots have more root hairs grown either way? What differences do you observe? The guide to Measuring Plant Growth can help you design ways to evaluate whether aquaponics is a viable method for growing plants.

Credits

Michelle Maranowski, PhD, Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Fish + Food = Science of Aquaponics" Science Buddies. Science Buddies, 7 Dec. 2012. Web. 21 Oct. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p032.shtml>

APA Style

Science Buddies Staff. (2012, December 7). Fish + Food = Science of Aquaponics. Retrieved October 21, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/EnvEng_p032.shtml

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Last edit date: 2012-12-07

Bibliography

The following website gives detailed instructions on how to construct a backyard aquaponics system. In addition, there is lots valuable information on aquaponics including a frequently asked questions page.

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