Aquaponics - Integration of Hydroponics with Aquaculture

Aquaponics is a bio-integrated system that links recirculating aquaculture with hydroponic vegetable, flower, or herb production. Recent advances by researchers and growers alike have turned aquaponics into a working model of sustainable food production. This publication provides an overview of aquaponics with brief profiles of working units around the country. An extensive list of resources point the reader to print and web-based educational materials for further technical assistance.

Aquaponics, also known as the integration of hydroponics with aquaculture, is gaining increased attention as a bio-integrated food production system.

Aquaponics helps production agriculture meet its goals of sustainability by following certain principles:

In aquaponics, nutrient wastes from fish tanks are used to fertilize hydroponic production beds via irrigation water. This is good for the fish because plant roots and associated rhizosphere bacteria remove nutrients from the water. These nutrients - generated from 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 so the water can then be recirculated back into the fish tanks. The bacteria living in the gravel and in association with the plant roots play a critical role in nutrient cycling; without these microorganisms the whole system would stop functioning. Greenhouse growers are taking note of aquaponics for several reasons:

The technology associated with aquaponics is complex. It requires the ability to simultaneously manage the production and marketing of two different agricultural products. Until the 1980s, most attempts at integrated hydroponics and aquaculture had limited success. However, innovations in the 1980s and 90s have transformed this technology into a viable modern food production system. This publication will not attempt to summarize the production details associated with aquaponics, but rather it will point to key innovators and published resources for further information.

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: 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 noncirculating water culture. Aggregate hydroponic systems employ inert, organic, and mixed media contained in bag, trough, trench, pipe, or bench setups. Aggregate media used in these systems include perlite, vermiculite, gravel, sand, expanded clay, peat, and sawdust. Normally, hydroponic plants are fertigated (soluble fertilizers injected into irrigation water) 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 hydroponic plants. However, in aquaponics, nutrients are delivered via aquacultural effluent. Fish effluent contains sufficient levels of ammonia, nitrate, nitrite, phosphorus, 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 density of fish tanks and subsequent nutrient concentration of aquacultural effluent. Lettuce, herbs, and specialty greens (spinach, chives, basil, and watercress) 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 to low light, high humidity conditions in greenhouses than field varieties.

Fish Species: Several warm-water and cold-water fish species are adapted to recirculating aquaculture systems, including tilapia, 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 recirculating 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. Barramundi and Murray cod fish species are raised in recirculating aquaponic systems in Australia.

Water Quality Characteristics: Fish raised in recirculating tank culture require good water quality conditions. Water quality testing kits from aquacultural supply companies are fundamental. 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.

Biofiltration and Suspended Solids: Aquaculture effluent contains nutrients, dissolved solids, and waste byproducts. Some aquaponic systems are designed with intermediate filters and cartridges to collect suspended solids 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.

Component Ratio: Matching the volume of fish tank water to volume of hydroponic media is known as component ratio. Early aquaponics systems were based on a ratio 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 (gravel vs. raft), fish species, fish density, feeding rate, plant species, etc. For example, the Speraneo system described below is designed for one cubic foot of water to two cubic feet of grow bed media (pea gravel). 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 ratio can favor greater outputs of either hydroponic produce or fish protein. A "node" is a configuration that links one fish tank to a certain number of hydroponic beds. Thus, one greenhouse may contain a multiple number of fish tanks and associated growing beds, each arranged in a separate node.