Category Archives: Sustainability

“Effect of plant species on nitrogen recovery in aquaponics” (Hu et al 2015)

Citation: Hu, Z., Lee, J., Chandran, K., Kim, S., Brotto, A., and Khanal, S.  (2015). “Effect of plant species on nitrogen recovery in aquaponics.” Bioresource Technology, 188, pp 92-98. DOI: 10.1016/j.biortech.2015.01.013

Summary By: Alexandra Pounds

Image Credit: Wikimedia Commons (Pak Choi) and Wikimedia Commons (Tomatos)

  • Big Picture: Tomato plants are better than pak choi at removing nitrogen from aquaponics systems because they have more root surface area that hosts nitrifying bacteria.
  • This study looked at how much nitrogen was removed from an aquaponics system by tomato (Lycopersicon esculentum) and pak choi (Brassica campestris L. subsp. chinensis). These plants were selected because one is a “fruity” plant (tomato) while the other is a “leafy” plant (pak choi).
  • Fish produce excess nitrogen as waste – releasing this into the environment can cause eutrophication & environmental problems. Aquaponics is seen as making fish farming environmentally-sustainable, because plants utilize the excess nitrogen that the fish produce as waste. How well the plants utilize this nitrogen is important.
  • Nitrifying bacteria that live on the surface area of plant roots help the plants uptake nitrogen. More root surface area means more space for nitrifying bacteria, which means that more nitrogen can be utilized by the plant.
  • Methods:
    • 2 aquaponics systems with tilapia (at high stocking densities) were run for 5 months in Hawaii, one with tomato plant, and one with pak choi. The fish were fed once per day.
    • water parameters and nitrogen levels were measured daily.
    • at the end of the trial, samples were dried and analysed for nitrogen content to complete a mass balance, allowing the researchers to calculate nitrogen released as gas.
  • Results:
    • Tomato was better at removing nitrogen (TAN and NO3-) than pak choi. The nitrogen utilization efficiencies (NUE) tells us how efficient the plant is at removing nitrogen.
      • NUE in tomato-based aquaponic systems: 41.3%
      • NUE in pak choi-based aquaponic systems: 34.4%
    • This was probably because there was 4.2 times more nitrifying bacteria in the tomato-based system. The tomato-based system probably had more nitrifying bacteria because it had a higher root surface area.
    • 1.5-1.9 % of the nitrogen was released as N20 gas (nitrous oxide, a “greenhouse gas” like CO2).
    • The tomato-based system also had better water quality, which resulted in greater fish growth and hence, a lower FCR.
    • Fish feed was the main source of nitrogen (99%).
    • “Gaseous nitrogen losses (NH3, N2O and N2) accounted for 51.2% and 57.3% of total N output in tomato- and pak choi- based aquaponics, respectively.”
  • Limitations:
    • The pak choi was harvested 3 times, whereas the tomatos were only harvested once (pak choi grows faster than tomatos). Roots are removed during harvesting, which disturbs the nitrifying bacteria. Tomatos could have had stronger NUEs because their nitrifying bacteria wasn’t disturbed.

“Food Production and Water Conservation in a Recirculating Aquaponic System in Saudi Arabia at Different Ratios of Fish Feed to Plants” (Al-Hafedh et al 2008)

Citation: Al-Hafedh, Y., Alam, A., Beltagi, M. (2008). “Food Production and Water Conservation in a Recirculating Aquaponic System in Saudi Arabia at Different Ratios of Fish Feed to Plants”. Journal of the World Aquaculture Society, 39(4), pp. 510-520. doi: 10.1111/j.1749-7345.2008.00181.x

Summary By: Alexandra Pounds

Image Credit: Wikimedia Commons

  • Big Picture: Recirculating Aquaponic system with Nile Tilapia and Leaf Lettuce produces more food and reuses more water than other systems in Saudi Arabia, like ponds or raceways.
  • This experiment used Nile Tilapia and Leaf lettuce in a recirculating aquaponics system to test different fish feed to plant ratios. Which ratio would maximize food production and water reuse within the system?
  • Methods:
    • Used commercial design with 3 parts: fish culture component, solid removal component, and hydroponic plant growing component for biofiltration
    • Plants were housed in Styrofoam rafts
    • Water was recirculated at 250 L/min.
    • Fish were stocked at 160 kg fish/m3
    • Fish were harvested every 6-8 weeks.
    • Plants were harvested every 4 weeks.
  • Results
    • The system effectively treated the water and plants effectively removed ammonia.
    • Fish had a 97.5% survival rate.
    • Tanks with all male fish had better production than tanks with mixed sex fish (male tilapia grow faster than female tilapia).
    • Only 1.4% of water needed to be added daily (compared to 20-25% in ponds, raceways, or flow-through systems) – the system managed to recycle 98% of its water.
    • production: 40 kg fish/m3 every 6 months
    • “A ratio of 56 g fish feed/m2 of hydroponic surface effectively controlled nutrient buildup in the effluents.

Best types of Plants for aquaponics:

  • Lower nutrient requirement plants which do better with lower fish stocking densities:
    • Lettuce (low-nutrient requirement)
    • Herbs
    • Specialty greens (spinach, chives, basil, and watercress)
  • Higher nutrient requirement plants which do better with higher fish stocking densities:
    • tomatoes
    • bell peppers
    • cucumbers

Marine species that have been grown successfully in aquaponics:

  • Nile tilapia, Oreochromis niloticus;
  • Hybrid tilapia, Oreochromis urolepis hornorum × Oreochromis mosambicus;
  • Koi carp, Cyprinus carpio;
  • Hybrid carp, Ctenopharyngodon idella × Aristichthys nobilis;
  • Hybrid striped bass, Morone chrysops × Morone saxatilis;
  • Goldfish, Carassius sp.
  • Rainbow trout, Oncorhynchus mykiss;
  • Australian barramundi, Lates calcarifer;
  • Murray cod, Maccullochella peelii peelii;
  • Red claw crayfish, Cherax quadricarinatus



“The Production of Catfish and Vegetables in an Aquaponic System” Mamat, Shaari, & Wahab 2016

Citation: Mamat, N., Shaari, M., and Wahab, N. (2016). “The Production of Catfish and Vegetables in an Aquaponic System”. Fisheries and Aquaculture Journal, 7(4). doi:10.4172/2150-3508.1000181

Summary By: Alexandra Pounds

Image Credit: Flikr

  • Big Picture: African catfish grow equally as well with red amaranth, green-red amaranth, and water spinach in an aquaponic system.
  • The study compared the growth rates of African Catfish (Clarias gariepinus) when cultured in aquaponic systems (systems that grow fish and plants in a recirculating water system). They compared three vegetables: red amaranth, green-red amaranth, and water spinach.
  • Methods:
    • System: They used 15 aquaponic systems in Malaysia. Each system had 80 gallons of water.
    • Fish: Each system held 15 African Catfish juveniles. The fish were fed twice daily with commercial pellets at 6% of their bodyweight per day. Fish were grown over 60 days. The fish were weighed weekly.
    • Plants: The vegetables were sown and sprouted before being transferred to the aquaponic system. vegetables were harvested after 30 days. Two sets of vegetables were grown off of one set of fish.
  • Results: Green-red amaranth produced the biggest fish, followed by fish co-cultured with both red amaranth and water spinach. However, none of the results were statistically significant.
  • Conclusion: The plant species didn’t affect the growth of the catfish.

“Increasing the Economical Efficiency and Sustainability of Indoor Fish Farming by Means of Aquaponics – Review” Blidariu & Grozea 2011

Citation: Blidariu, F. and Grozea, A. (2011). “Increasing the Economical Efficiency and Sustainability of Indoor Fish Farming by Means of Aquaponics – Review.” Animal Science and Biotechnologies, 44(2), pp. 1-8.

Summary by: Alexandra Pounds

Image Credit: Wikimedia Commons

  • Big Picture: Combining fish culture with plant farming (aquaponics) is a sustainable and environmental friendly way to produce high quality food. Aquaponics could make indoor fish farming more sustainable by reducing waste production.
  • “Aquaponics”: indoor fish farm + hydroponic plants (plants that are grown in nutrient-rich water rather than soil)
  • Recirculating Aquaculture Systems (RAS, aka “indoor fish farms”) are the most commonly used for aquaponic systems.
  • RAS are the most environmentally friendly systems in aquaculture because unlike flow-through systems, wastewater is cleaned and reused rather than discarded. It allows for greater control over biosecurity (risk of disease) and quality. They are criticised because they still produce a lot of waste products.
    • Removal efficiency of traditional RAS for organic/fecal matter: 85-95%
    • Removal efficiency of traditional RAS for phosphorus: 65-96%
  • Instead of discarding this waste, why not use the waste as plant fertilizer? Instead of mechanical treatment systems and filters, plants biofilter the wastewater so that it can be reused for the fish. Fish waste provides nutrients that the plant would otherwise get through soil or fertilizer. The farmer can sell both plants and fish.
  • Plants solve multiple problems in RAS farming:
    • Ammonia/Nitrogen/Carbon Dioxide toxicity: Fish produce ammonia & carbon dioxide as waste, but both are toxic to them. Plants remove ammonia from the water and convert it to nitrite, which the plant uses for growth along with carbon dioxide. Fish can tolerate much higher concentrations of nitrite than ammonia. This paper reports that plants can remove ammonia at a 86-98% efficiency.
    • Oxygen depletion: Fish need oxygen, and water can become depleted. Farmers usually have to add oxygen to the water in RAS. Plants produce oxygen as a by-product, which can be added back to the water for the fish.
  • These systems could be used in small-scale urban farming, for example, on rooftops or in gardens in over-populated urban areas that may have reduced access to water. It is debated whether aquaponics can be profitable on a commercial scale.
  • Challenges:
    • Aquaponic farmers must balance the amount of plants with the amount of fish. There must be enough plants to manage the amount of waste that the fish produce. Likewise, there must be enough fecal waste from the fish to fertilize the plants. It is its own ecosystem.
    • Fish require high flow rates of water, which results in low concentrations of effluent (waste in the water). Plants require high concentrations of effluent.
    • Aquaponics cannot use pesticides because pesticides are toxic to fish. Similarly, many treatments for fish disease would be absorbed by the plants, creating human-consumption safety issues. Aquaponics requires “natural” treatments.
  • Benefits:
    • Two products (fish and plants) = investment diversity. If one has poor yield, farmer still has the other to mitigate losses.
    • Reduces costs of fertilization and filtration equipment. Infrastructural equipment costs are shared, which can lower the overall COGs (cost of goods sold = how much is costs to produce the product).
    • Space efficient.
    • Easy to certify as organic & environmentally sustainable.
    • Can be marketed as locally produced, even in heavily populated cities with colder climates.
    • Potentially faster growth rates with higher and more consistent quality.
    • Decreased waste production.
    • Can be adapted for farmers with disabilities.
  • The best plants for aquaponics are those that require low levels of nutrients, such as: lettuce, herbs, spinach, chives, basil, watercress. Plants with high-nutrient demands (like tomatos, bell peppers, and cucumbers) would require more intensive systems with more fish production.
  • The best fish for aquaponics are hardy fish like catfish or tilapia.