Sustainable Multitrophic Fish And Vegetable Production With Aquaponics

In the crowded world, humans have not yet made enough strategies to manage the land and water resources for future development. Almost one billion people are undernourished in the present era, particularly in Sub-Saharan Africa (239 million) and Asia (578 million). Moreover, agricultural production if doubles by 2050 in the developing countries, in spite of this, one person in twenty will in risk of undernourished, most of whom will again be from Africa and Asia.

Importance of Water

Water is an important component for every form of life and becoming a more worth commodity than oil because, only 0.003% amount of fresh water available for drinking, hygiene, agriculture, and industrial activities.  Globally, 60% more food will be required by 2050 to meet the ever-increasing population’s nutrition requirements; therefore, water demand will be further increased.

India’s population is likely to be 1.6 billion by 2050, resulting in increased demand for water, food, and energy, whereas the supply of resources is more or less constant. India retains only 4% of the world’s freshwater resources and is considered a water-stressed country, with 1544 m3 per capita water availability, which likely to become a water-scarce because per capita water availability will go down to 1341 m3 and 1140 m3 by 2025 and 2050, respectively. Therefore, eco-friendly food production has to be initiate with sustainable utilization of natural resources.

Importance of Fisheries

Globally, fisheries play an important role in protein production, and expansion of this sector, reducing the pressure on less sustainable terrestrial farming systems. Aquaculture is now escalating the world’s fisheries through four major culture methods, open water systems (cage, pen, and raft), pond culture, flow-through raceway, recirculating aquaculture system (RAS).

All these methods have an issue of nutrient-rich wastewater management, and without any treatments, the release of wastewater tends to eutrophication, hypoxia, and biodiversity depletion of the natural ecosystem.

Aquaponics is a sustainable integrated technique of growing soil-less plants that is hydroponic with aquaculture. This technology is able to solve major issues of aquaculture by drop-down the water uses by 80% and prevents the release of hazardous wastewater into the surrounding ecosystem. It helps to gain more economic benefit by growing the plant within the nutrient-rich effluent of aquaculture, which alike qualifies under current guidelines for “organic” and thus fetches a higher market price for the product.

Aquaponic Technology 

Aquaponics is a self-supporting food production system that integrates aquaculture with soil-less plant culture (hydroponics). The development of such an integrated system reduces the cost of effluent discharge from aquaculture and expensive chemical fertilizer use in the production of plants through hydroponic systems. It can be more productive and economically worthwhile in certain circumstances, especially where land and water are limited.

In an aquaponic system, aquaculture effluents are moving through the plant’s growing bed and preventing releases into the environment, whereas another side the plants are getting cost-effective and non-chemical nutrients from the waste. In this system, nutrient-rich water from the fish culture tank circulates through filters, plant grow beds, and then drives back clean water to the fish tank.

Mechanical and bio-filter are used to remove solid and dissolved fish waste, and during the biofiltration, beneficial bacteria convert the metabolic fish waste into more accessible nutrients for plants and finally plants uptake these nutrients. Such kind of integrating system solves the unsustainable factors of running aquaculture and hydroponic systems independently.

 Important Biological Components of Aquaponic System

a). Bio-filter: In an aquaponics system, metabolic fish waste passes through a bio-filter that provides a habitat for bacteria to oxidize the toxic ammonia into accessible nutrients for plants. The bio-filter prevents the water become toxic to nitrogenous metabolites and allows the fish, plants, and bacteria to thrive symbiotically in a healthy environment. In an aquaponic system, fish excreta (NH3) released in the culture tanks is converted by specific nitrifying bacteria into nitrite compounds and then finally into nitrate compounds via nitrification, which is used by plant as nutrient.

b). Suitable Fish Species For Aquaponics: All the fish species are not suitable in the aquaponic system; it depends on the fish biology, behavior, and tolerance to water parameters. Though seasonal air temperature, stocking density, and water quality parameters determine what species should be raised in the system. Fish species include tilapia, carps (common, koi, silver, and grass), barramundi; jade perch, flathead mullet, channel catfish, African catfish, trout, salmon, largemouth bass, and Giant River prawn have shown better growth in aquaponics.

c). Suitable Plants For Aquaponics: Like fish, all plants are not suitable for the aquaponics system; around 150 different vegetables, herbs, flowers, and small trees have been grown successfully for research, domestic and commercial purposes. Based on the market, producers often grow leafy greens and herbs like lettuce, chard, salad rocket, basil, mint, parsley, coriander, chives, pak choi, spinach and watercress, which have high production with low nutrient demand. Plants with medium to high nutrient demands are cabbages, cauliflower, broccoli, kohlrabi, legumes, and fruiting crops such as peas, beans, tomatoes, eggplants, cucumbers, strawberries, and peppers.

Water quality in aquaponics Water is the important component of an aquaponic system, because all essential nutrients are transported through water. Important water quality parameters and their specific tolerance limit to the organism are given in table 1&2. Water with salinity above 0.8 ppt is typically not suitable for aquaponic production as the majority of cultured plants do not tolerate even a small degree of salt.

Types of The Aquaponics

Based on the design, aquaponics classified into; Media-Based Systems, Deep Water Culture and Nutrient Film Technique.

a) Media-based Systems (MBS): MBS is one of the simplest aquaponic systems, and it is also called a flood-and-drain system. In this, a container filled with the substrate (gravel, lava rock, clay pebbles or locally available media) is time to time flooded with fish tank water and then drain ammonia-free water back to the fish tank (fig 3). The substrate filled in a container work as a bio-filter and also provides support to plants. Water flow in this system can be controlled by a timer or automatic siphon mechanism. MBS is not suitable at the commercial production level.

b) Deep Water Culture (DWC): In this design, plants are suspending in a floating raft and roots to hang down into the nutrient-rich water that comes from the fish tank. The DWC provides a large water holding capacity, where water lining below the raft offers sufficient space to beneficial bacteria. Effective filtration and aeration are required to prevent solid waste into the plant bed and adequate oxygen levels for plant roots and bacteria. The DWC is more productive than MBS, and it is commercially functional on large-scale production of vegetables.

c) Nutrient Film Technique (NFT): The NFT was established by the hydroponics industry, where plants are growing into the top of shallow horizontal channels, and nutrient-rich water is continuously pumped through these channels. The NFT like DWC, requires sufficient solids filtration to prevent contamination of plant roots. In contrast to DWC, NFT systems need a separate biological filter, as the channel alone does not provide enough surface area for sufficient growth of nitrifying bacteria. The NFT is complex to design, build, and manage because plant roots can interrupt water flow in the channels. However, it can be a great system for urban areas or rooftops as they are lightweight, use very little water, and can be made from easily sourced materials.

Source: Singh, Jaspreet & Kumar, Tarkeshwar & Sarma, Kamal & Ahirwal, Surendra. (2021). Aquaponics: Toward a Sustainable Multi-trophic Production of Fish and Vegetables. 2. 46.

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