Aquaponics, also known as the integration of hydroponics with aquaculture, is gaining increased attention as a bio-integrated food production system. Aquaponics serves as a model of sustainable food production by following certain principles:
- The waste products of one biological system serve as nutrients for a second biological system.
- The integration of fish and plants results in a poly culture that increases diversity and yields multiple products.
- Water is re-used through biological filtration and recirculation.
- Local food production provides access to healthy foods and enhances the local economy.
In aquaponics, nutrient-rich effluent from fish tanks is used to fertigate hydroponic production beds. This is good for the fish because plant roots and rhizobacteria remove nutrients from the water. These nutrients generated form fish manure, algae, and decomposing fish feed-are contaminants that would otherwise build up to toxic levels in the fish tanks, but instead serve as liquid fertilizer to hydroponically grown plants. In turn, the hydroponic beds function as a biofilter – stripping off ammonia, nitrates, nitrites, and phosphorus – so the freshly cleaned water can then be re-circulated back into the fish tanks. The nitrifying bacteria living in the garvel and in association with the plant roots play a critical role in nutrient cycling; without these microorganisms the whole system would stop functioning.
Green house growers and farmers are taking note of aquaponics for several reasons:
- Hyrdroponics growers view fishmanured irrigation water as a source of organic fertilizer that enables plants to grow well.
- Fish farmers view hydroponics as a bio-filtration method to facilitate intensive re-circulating aqua culture
- Green house growers view aquaponics as a way to introduce organic hydroponic produce into the market place, since the only fertility input is fish feed and all of the nutrients pass through a biological process.
- Food- producing greenhouses – yielding two products from one production unit- are naturally appealing for niche marketing and green labeling.
- Aquaponics can enable the production of fresh vegetables and fish protein in arid regions and on water limited farms, since it is water re-use system.
Aquaponics is a working model of sustainable food production where in plant and animal agriculture is integrated and recycling of nutrients and water filtration is linked.
In addition to commercial application, aquaponics has become a popular training aid on integrated bio-systems with vocational agriculture programs and high school biology classes.
The Technology associated with aquaponics is complex. It requires the ability to simultaneously mange the production and marketing of two different agricultural products. Until the 1980’s, most attempts at integrated hydroponics and aquaculture had limited success.
However, innovation since the 1980’s has transformed aquaponics technology into a viable system of food production. Modern aquaponic systems can be highly successful, but they require intensive management and they have special considerations.
Aquaponics: Key Elements and Considerations
A successful aquaponics enterprise requires special training, skills and management. The following items point to key elements and considerations to help prospective growers evaluate the integration of hydroponics with aquaculture.
Hydroponics is the production of plants in a soilless medium whereby all of the nutrients supplied to the crop are dissolved in water. Liquid hydroponic systems employ the nutrient film technique (NFT), floating rafts, and non circulating water culture. Aggregate hydroponic systems employ inert, organic, and mixed media contained in bag, trough, trench, pipe, or bench setups. Aggregate media used n these systems include perlite, vermiculite, gravel, sand expanded clay, peat, and sawdust. Normally, hydroponic plants are fertigated on a periodical cycle to maintain moist roots and provide a constant supply of nutrients. These hydroponic nutrients are usually derived from synthetic commercial fertilizers, such as calcium nitrate, that are highly soluble in water. However, hydro organics – based on soluble organic fertilizers such as fish hydrosylate – is an emerging practice. Hydroponic recipes are based on chemical formulations that deliver precise concentrations of mineral elements. The controlled delivery of nutrients, water, and environmental modifications under greenhouse conditions is a major reason why hydroponics is so successful.
Nutrients in Aquaculture Effluent:
Greenhouse growers normally control the delivery of precise quantities of mineral elements to hydroponics plants. However, in aquaponics, nutrients are delivered via aqua cultural effluent. Fish effluent contains sufficient levels of ammonia, nitrate, nitrite, phosphorous, potassium, and other secondary and micronutrients to produce hydroponic plants. Naturally, some plant species are better adapted to this system than others.
Plants Adapted to Aquaponics:
The selection of plant species adapted to hydroponic culture in aquaponic greenhouses is related to stocking of fish tanks and subsequent nutrient concentration of aqua cultural effluent. Lettuce, herbs, and specially greens (spinach, chives, basil, and water access) have low to medium nutritional requirements and are well adapted to aquaponic systems. Plants yielding fruit (tomatoes, bell peppers, and cucumbers) have a higher nutritional demand and perform better in a heavily stocked, well established aquaponic system. Greenhouse varieties of tomatoes are better adapted low light, humidity condition in greenhouses then field varieties.
Several warm-water and coldwater fish species are adapted to re-circulating aquaculture systems, including tilapis, trout, perch, Arctic char, and bass. However, most commercial aquaponic systems in North America are based on tilapia. Tilapia is a warm-water species that grows well in a re-circulating tank culture. Furthermore, tilapia is tolerant of fluctuating water conditions such as pH, temperature, oxygen, and dissolved solids. Tilapia produces a white fleshed meat suitable to local and wholesale markets. The literature on tilapia contains extensive technical documentation and cultural procedures. Barramundi and Murray cod fish species are raised in re-circulating aquaponic systems in Australia.
Water Quality Characteristics:
Fish raised in re-circulating tank culture require good water quality conditions. Critical water quality parameters include dissolved oxygen, carbon dioxide, ammonia, nitrate, nitrite, pH, chlorine, and other characteristics. The stocking density of fish, growth rate of fish feeding rate and volume, and related environmental fluctuations can elicit rapid changes in water quality; constant and vigilant water quality monitoring is essential.
Bio-filtration and Suspended Solids:
Aquaculture effluent contains nutrients, dissolved solids, and waste by products. Some aquaponic systems are designed with intermediate filters and cartridges to collect suspended solid in fish effluent and to facilitate conversion of ammonia and other waste products to forms more available to plants prior to delivery to hydroponic vegetable beds. Other systems deliver fish effluent directly to gravel-cultured hydroponic vegetable beds. The gravel functions as a “fluidized bed bioreactor,” removing dissolved solids and providing habitat for nitrifying bacteria involved in nutrient conversions.
Matching the volume of fish tank water to volume of hydroponic media is known as component ratio. Early aquaponics systems were based on a ration of 1:1, but 1:2 is now common and tank: bed ratios as high as 1:4 are employed. The variation in range depends on type of hydroponic system, fish species, fish density, feeding rate, plant species, etc. Further, when shallow bed systems only three inches in depth are employed for the production of specialty greens such as lettuce and basil, the square footage of grow space will increase four times. Depending on the system design, the component ration can favor greater outputs of either hydroponics produce or fish protein. A “node” is a configuration that links one fish tank to a certain number of hydroponics beds. Thus, one greenhouse may contain a multiple number of fish tanks and associated growing beds, each arranged in a separate node.
Prospect of Aquaponics for the future
Aquaponics has become very popular in recent years, but it is still in its infancy and is being practiced mainly at the hobby and backyard levels. It is estimated that there are 1,500 aquaponic systems in the United States and many times this level in Australia. However, the number of commercial operations is still relatively small in the United States. Hydroponic growers generally do not consider aquaculture as nutrient source for their operations. Aqua culturists, on the other hand, frequently mention the possibility of incorporating hydroponics into their closed re circulating systems to mitigate waste discharge and earn extra income. Data from successful, large scale trials are needs to attract investor capital and spur commercial development.
Source: Aqua Aquaria