Dan Burden, AgMRC Content Specialist
D. Allen Pattillo, Department of Natural Resources Ecology & Management, Iowa State University; North Central Regional Aquaculture Center (NRAC)
Aquaponics is a hybrid food growing technology that combines aquaculture (growing fish) and hydroponics (growing veggies in non-soil media and nutrient-laden water). This is a relatively new hybrid technology; a survey of readily available professional and hobbyist Internet resources will quickly give one an appreciation of the wide breadth of and passion for this technology.
Aquaponics is intended to be a highly sustainable production system that incorporates principles of water conservation, sustainable vegetable production and perhaps organic plant and animal agriculture. Systems vary in size from small indoor or outdoor home or classroom hobbyist units to immense commercial units. The systems are usually fresh-water based, but salt-water systems are used for some high-value fish or crustacean production. It should be noted that the corrosive effects of salt-water can greatly increase the establishment, maintenance and depreciation costs of the production system.
In traditional tank-type aquaculture systems, the fish are raised within a mostly closed system where water is recirculated. Since it is a closed system, filters are required to remove fish effluent and remove aqueous toxic compounds that result from the effluent or its decomposition. If not removed, the effluent and its toxic nitrogenous bi-products quickly reach levels that are fatal to fish. In aquaponics systems, the effluent is as passively managed as possible within the system using sumps and biofilters. Some solids may be physically separated and removed; however, the majority of the toxic compounds are biologically converted into plant-usable nutrients through bio-conversion by beneficial bacteria within the biofilter. This nutrient-laden water is now the fertilizer component of the plant aspect of the system. The plants then remove the nutrients and the “de-nitrified” clean water is returned back to the fish, crustacean or mollusk aspect of the system as their water input.
An intermediate-scale pre-commercial aquaponic system.
The systems are highly sustainable and can be highly efficient to operate. To create maximum efficiency and the highest return-on-investment (ROI) in a commercial system, energy inputs in terms of lighting (for the plants), aeration (for the fish) and pumps or uplift systems (overall system recirculation) should be carefully considered and reflected in the design of the system. It is easy to build a working system. It is challenging to fine-tune that system for maximum efficiency (lowest-cost and lowest-human-intervention operation; highest sustainability), maximum highest-quality plant production and best fish, crustacean or mollusk growth rate and health.
This closed-loop system has many advantages over conventional “open-loop” crop production systems:
- It uses approximately 10% of the land area and 5% of the water volume required by conventional vegetable crops.
- Due to less water and land use, aquaponics is perfect for highly efficient use of existing space or for special applications like intensive urban gardening.
- Crop production time can be accelerated. For example, butterhead lettuce varieties can be produced in about 30 days, instead of the typical 60-day growing period needed for conventional production.
- Production can occur year-round under a greenhouse or in a temperature-controlled enclosure. This allows producers to market fresh produce during seasons when trucked-in produce is at their highest seasonal prices.
- Aquaponics is an adaptable process that allows for a diversification of income streams. High-value herbs, vegetables, and leafy greens, as well as fish, crayfish, worms, mushrooms, and a number of other crops may be produced, depending upon local market interest and the interests of the grower.
- These systems allow agriculture to take large innovative steps toward environmental sustainability. Because these are mostly-closed-loop systems, nutrient effluent leaving the facility is virtually nonexistent. Additionally, fish, plant, and other waste solids may be captured and converted into value-added fertilizer products for wholesale or retail sale.
- Growers can start small, with minimal investment, perhaps using scrounged materials to see if the venture is “right for me,” then scale-up as markets and expertise develops.
There are many fish, crustacean or mollusk species that are well suited to aquaponic systems. With respect to fish species, tilapia and barramundi are fast-growing species well suited to the water temperatures of most aquaponic systems. Other species, e.g., trout, hybrid-striped bass, bluegills, yellow perch or ornamental species like koi or pet-trade cichlids can be raised in these systems, but each species presents its own set of unique challenges and unique markets. Crustaceans include fresh-water, salt-water and brackish-water shrimp and prawns, and crayfish. Mollusks (snails) have been raised in some systems.
There are four major types of plant growth subsystems. These include:
- Ebb and Flow - This method, also known as flood-and-drain culture, requires the use of a substrate, like pea gravel or expanded clay, for the plant roots to grow in for stability. This method uses a constant inflow of water and auto-siphon device to flood then quickly drain the grow bed, usually on a 20- to 30-minute cycle. This periodic water emersion and air exposure produces an environment highly conducive to healthy plant root systems. This method has the advantage of structural support for larger and heavier fruiting plants, like peppers or tomatoes, that otherwise could be problematic.
- Deep-water Culture This method, also known as floating-raft culture, requires the use of a platform to support the plants and holes for the roots to access the water. Styrofoam insulation is typically used as the raft and plastic net pots support the plants. Aeration should be supplied via air stones in the water under the raft to ensure a high oxygen concentration should the water cease to circulate or become stagnant. The larger volume of water required for this method has benefits. It increases overall stability in temperature and water quality, which translates to lower overall maintenance and greater system stability.
- Nutrient Film Technique (NFT) This method of plant culture allows the plant root systems to absorb nutrients from a thin film of water (up to ½-inch depth), while maintaining high oxygen exposure through high atmospheric air contact. NFT is typically done by emitting a small amount of water into one end of a channel or gutter, and allowing that water to flow by gravity to the other end where it drains into a common collection area. Because of the high potential surface area, this method allows for greater plant production with less water.
- Drip Irrigation This method uses drip emitters to provide a constant supply of nutrient-rich water to plant root systems, contained in large buckets of substrate, usually expanded clay or slabs of rock wool. This method is very well suited to the production of fruiting, vine-type plants that can be grown continuously for multiple years, like cucumbers, tomatoes or some tropical fruits. Plants generally are ‘trained’ to grow onto a trellis or similar structure for ease of harvest and maintenance. An advantage to drip irrigation is the more inherently modular design. If one plant dies or becomes diseased, it is easy to remove that plant or unit of plants and disinfect the area without sacrificing the entire crop. Also, this method works well for large, heavy plants that need to sit on the floor, perhaps in a large pot. Although in a large substrate container, the plant and its support infrastructure can easily be maintained, repositioned or modified.
There are hundreds of ways to build an aquaponics system. Systems can be successful as a hobby-scale installation in a garage or basement, seasonally in the backyard or on the deck, or as full-blown commercial-scale ventures. The critical considerations for any producer are: the amount of available space; the amount of available money for the project; the intent for and amount of food to be produced; and if a commercial venture, how the products will be marketed. Aquaponically grown products, like other fish or produce, are highly perishable; it is important to keep in mind that harvest- and post-harvest handling and related marketing considerations are critical components of any aquaponics business plan.
Aquaponics overview from Growing Power a community group in Wisconsin
Aquaponics How To
Do It Yourself Aquaponics
NCRAC: North Central Regional Aquaculture Center
Nelson &Pade a commercial system supplier.
The Aquaponics Source.Com
Wikipedia overview of aquaponics
Links checked: August 2013.