Editor: Ragnheidur I. Thorarinsdottir
Editor: Ragnheidur I. Thorarinsdottir
Printed by Haskolaprent, Reykjavik, Iceland
Layout: Anna Maria Proppe
Dr. Ragnheidur Thorarinsdottir, Svinna-verkfraedi Ltd, www.svinna.is and University of Iceland
Dr. Paul Rye Kledal, IGFF, Denmark, www.igff.dk
Siv Lene Gangenes Skar, Nibio, Norway, www.nibio.no
Fernando Sustaeta, Breen, Spain, www.breen.es
Dr. Kristin Vala Ragnarsdottir, University of Iceland, www.hi.is, earthice.is
Dr. Utra Mankasingh, www.hi.is
Dr. Edoardo Pantanella, Eureka, Italy, www.eurekafarming.com
Rob van de Ven, LandIng Aquaculture, Netherlands, www.landingaquaculture.com
R. Charlie Shultz, Texas, USA, www.globalaquaponics.net
Special thanks to:
Dr. Ranka Junge, ZHAW, Switzerland, www.zhaw.ch, Dr. Vesna Milicic, Ponika
www.ponnod.com and University of Ljubljana, Slovenia, www.uni-lj.si and Dr. Harry Palm,
University Rostock, Germany, www.uni-rostock.de for providing information and pictures from
their aquaponic systems.
Aquaponics is a combination of the words aquaculture (cultivating fish) and
hydroponics (growing plants in water without soil) and the eco-innovative
technology behind the concept is a combination of the two production systems into
one. It is driven by a microbial ecosystem that assists in converting fish effluents into
usable plant nutrients while helping deliver plant nutrients across root cell walls. In
an aquaponic system, water is kept in circulation. Waste water from the fish is used
as nutrients in the horticultural part of the system where plants take up the nutrients
provided by the fish waste and cleanse the water before being returned to the fish.
Aquaponics is a resource efficient closed loop food production system, mimicking
nature itself. This relates to cradle-to-cradle design presenting eco-effectiveness
moving beyond zero emissions and produce services and products taking into
account social, economic and environmental benefits (McDonough and Braungart,
2002; Braungart et al., 2007; Kumar and Putnam, 2008).
Small private and/or educational/research aquaponic systems have been built in
several places around the world and the technology is becoming increasingly
popular. There is rising interest for industrial show cases, to test whether it can be a
profitable business to run large-scale aquaponic systems, raising fish and plants
simultaneously for the market. Commercial-scale facilities, although limited in
number, can now be found across the globe that incorporate modern technology
based on automatic control, improved system balance and health and safety.
The conditions to implement an aquaponics industry in Europe are currently being
evaluated and several pilot units of different sizes and design have been constructed
in most European countries. Only very few of them reach a production area of more
than a few square meters (m2). However, systems are now planned or have been
built on a medium scale of a few hundreds and up to a few thousand m2.
These guidelines present a short history of aquaponics as well as the current status of
aquaponics development in Europe. The main types of aquaponics system design are
outlined along with guidelines for how the environmental parameters need to be
controlled. Moreover, in this guiding document the production parameters are
described, including suitable choices of plants and fish species. The market
conditions, certification and regulatory issues are discussed, also including added
value opportunities linked to experience and educational tourism, technology
development and byproducts, e.g. from sludge processing. Finally, conclusions and
future perspectives are put forward.
It is the hope of the authors that the guidelines can be of value to aquaponics
hobbyists as well as others who plan to develop commercial scale aquaponics. The
guidelines are built on collaborative work between two European projects: the
Leonardo project EuroPonics (www.aquaponics.is/europonics) that focuses on
vocational training in aquaponics and the EASME project EcoPonics
(www.aquaponics.is/ecoponics/) which aims to establish commercial aquaponics in
Europe. Further contributors are aquaponics specialists from the management
committee of the COST Action FA1305 The EU Aquaponics Hub – Realising
Sustainable Integrated Fish and Vegetable Production for the EU
Keywords: Aquaponics, aquaculture, hydroponics, zero-waste, renewable energy,
Summary ............................................................................................................................ 5
List of figures ..................................................................................................................... 9
Acknowledgements ........................................................................................................ 10
1 Introduction – What is aquaponics?........................................................................ 9
2 History of aquaponics ............................................................................................. 12
2.1 University of Virgin Islands (UVI) ................................................................... 12
2.2 Developing units in Europe ............................................................................14
2.3 Decoupled systems ......................................................................................... 21
3 System description ................................................................................................ 22
3.1 Recirculating aquaculture system (RAS) ...................................................... 22
3.2 Mechanical filtration ...................................................................................... 22
3.3 Biofiltration .................................................................................................... 26
3.4 Hydroponics ................................................................................................... 29
3.4.1 Grow beds .............................................................................................. 31
3.4.2 Nutrient film technique (NFT) ............................................................... 31
3.4.3 Raft / deep water culture (DWC) .......................................................... 32
4 System control and optimization .......................................................................... 33
4.1 Controlling environmental parameters ........................................................ 33
4.2 Temperature .................................................................................................. 34
4.3 Dissolved oxygen ........................................................................................... 34
4.4 Chemical oxygen demand and biochemical oxygen demand ..................... 35
4.5 pH ................................................................................................................... 35
4.6 Alkalinity ......................................................................................................... 36
4.7 Nitrogen compounds ..................................................................................... 37
4.8 Electrical conductivity .................................................................................... 38
4.9 Macro- and micronutrients ............................................................................ 39
5 Production management ...................................................................................... 42
5.1 Choices of species – fish ................................................................................ 43
5.2 Choices of species – plants ............................................................................ 45
5.3 Quality and production of edible plants ....................................................... 47
5.4 Societal factors .............................................................................................. 49
5.5 Risk analysis ................................................................................................... 49
6 Market and certifications ....................................................................................... 51
6.1 Organic certification ...................................................................................... 52
6.1.1 Horticultural produce ........................................................................... 52
6.1.2 Aquacultural produce ........................................................................... 52
6.1.3 Future of organic aquaponics .............................................................. 53
7 Added value ........................................................................................................... 55
8 Conclusion and future perspectives ..................................................................... 57
References ....................................................................................................................... 58
List of figures
Figure 1.1 Aquaponic system ............................................................................................. 9
Figure 1.2 Decoupled aquaponic system ........................................................................ 10
Figure 2.1 UVI aquaponic system diagram (Rakocy et al., 1997) .................................... 13
Figure 2.2 Breen aquaponics pilot unit in Hondarribia, Spain ........................................14
Figure 2.3 Hatching facilities at Tknika ............................................................................14
Figure 2.4 New 6,000 m2 commercial aquaponics farm under construction ................ 15
Figure 2.5 IGFF aquaponics pilot unit .............................................................................. 15
Figure 2.6 Schematic diagram of the IGFF aquaponics pilot unit ................................. 16
Figure 2.7 Bio-filter, UV-lighting, sedimentation tanks and airblower .......................... 16
Figure 2.8 Svinna aquaponics pilot unit in Laugaras, Iceland ......................................... 17
Figure 2.9 Nibio aquaponics pilot unit in Grimstad, Norway ......................................... 18
Figure 2.10 Ponika aquaponics pilot unit in Prekmurje, Slovenia .................................. 18
Figure 2.11 Eureka farm R&D unit near Rome, Italy ....................................................... 19
Figure 2.12 FishGlassHouse ............................................................................................. 19
Figure 2.13 Decoupled system at IGFF ............................................................................. 21
Figure 3.1 Schematic overview of a recirculating aquaculture system (RAS) .............. 22
Figure 3.2 Sedimentation tank (left) and drum filter (right) ......................................... 24
Figure 3.3 Bead filter, trickling filter, moving bed bioreactor and swirl separator ...... 29
Figure 3.4 From left: Media bed, nutrient film and floating raft aquaponics ............... 30
Figure 3.5 Grow-beds at Breen ........................................................................................ 31
Figure 3.6 Nutrient film technique with okra plants ...................................................... 31
Figure 3.7 Floating system / deep water culture (DWC) ................................................ 32
Figure 4.1 Schematic representation of the N cycle in aquatic system ........................ 38
Figure 4.2 Potassium deficiency in a tomato plant ........................................................ 40
Figure 4.3 Calcium deficiency affecting tomato production ......................................... 40
Figure 4.4 Iron deficiency in an okra plant ......................................................................41
Figure 5.1 Nile Tilapia ....................................................................................................... 43
Figure 5.2 Lettuce (Lactuca sativa) produced at Nibio in Grimstad .............................. 45
Figure 5.3 Okra and pak-choi produced by Svinna in Reykjavik .................................... 45
Figure 5.4 Annual production kg per square meter of leafy greens in aquaponics
(Savidov, 2010) ................................................................................................................ 46
Figure 5.5 Root rot from phytium (left) vs healthy roots (right) .................................. 48
Figure 7.1 Red claw crayfish (Cherax quadricarinatus) from Svinna´s pilot unit .......... 55
Figure 7.2 Worm cultivation at Breen ............................................................................. 55
Special thanks are given to the following persons for supplying photos, schematic
pictures and good advice.
Ragnar Ingi Danner: 2.8, 7.1
Marvin Ingi Einarsson: 1.1, 1.2, 2.8, 3.1
Siv Lene Gangenes Skar: 2.9, 3.5, 5.2
Dr. Paul Rye Kledal: 2.5, 2.6, 2.7, 2.13
Ulrich Ricardo Knaus: 2.12
Soffia K Magnusdottir: 5.1
Dr. Vesna Milicic: 2.10
Dr. Olafur P Palsson: 2.4, 3.2, 3.3, 3.4, 3.6, 4.2, 4.4, 5.3
Dr. Edoardo Pantanella: 2.11
R. Charlie Shultz: 3.7, 5.5
Fernando Sustaeta: 2.2, 2.3, 3.4, 4.3, 7.2
1 Introduction – What is aquaponics?
Aquaponics is a food production method for producing terrestrial plants and aquatic
organisms that combines two traditional production systems – recirculating
aquaculture and hydroponics. Aquaponic systems recirculate and recycle all the
water and nutrients through symbiotic processes preventing discharge of eutrophic
or organic wastes. In November 2010, The Aquaponics Gardening Community
forward the following definition:
Aquaponics is the cultivation of fish and plants together in a constructed,
recirculating ecosystem utilizing natural bacterial cycles to convert fish
waste to plant nutrition. This is an environmentally friendly, natural food-
growing method that harnesses the best attributes of aquaculture and
hydroponics without the need to discard any water or filtrate or add
Aquaponics is an ecosystem of plants, fish, bacteria, sometimes worms and/or other
organisms, growing together symbiotically (Figure 1.1). The beneficial bacteria
convert the waste water from the fish into plant food, and the plants filter the waste
water for nutrients before the water returns back to the fish.
Figure 1.1 Aquaponic system
Many of today’s aquaponic systems circulate water and nutrients from fish to plants
to fish as shown in Figure 1.1 and the water quality is specifically managed to fit the
requirements of the fish species being cultured and suitable plants are chosen to fit
Introduction – What is aquaponics?
the fish environment. It is not always guaranteed that the fish preferences are
completely aligned with the optimum requirements of the plants. This calls for
compromising of the plant’s needs, and as a result they may not achieve their full
growth capacity. Therefore another design has been investigated in which the water
flow is divided into two independent systems that can occasionally communicate
whenever plants need a boost in nutrients or fish require reclaimed water from
plants to dilute the wastes accumulating in the fish sub-unit. This solution, which is
referred to as a “decoupled” system (Figure 1.2) would better secure optimal
environmental conditions for both the plant and fish production units and may
become a cornerstone towards the implementation of large commercial aquaponic
systems. The risk mitigation factor alone has increased the use of decoupled systems
globally. If a problem occurs in the fish or the plant components, each section can be
isolated and run as a stand-alone aquaculture or hydroponic system, while the
problem is addressed.
Figure 1.2 Decoupled aquaponic system
Many options exist for solid waste management in aquaponic systems. Discharged
solid wastes may be utilized to create value added products such as compost or on-
farm seeding media (Danaher et al., 2011; Pantanella et al., 2011a). Solids can also be
mineralized in a separate loop, allowing dissolved nutrients to be returned to the
system. Rakocy et al. (2005) described mineralization rates of discharged effluents
from an aquaponic system operated in the US Virgin Islands. Several ideas are being
tested aiming for zero-waste solutions, using the sludge as e.g. feed for crayfish,
farming of worms and/or black soldier flies, or making fertilizer or biogas through
aerobic or anaerobic digestion.
History of aquaponics
2 History of aquaponics
Aquaponic systems have been developing and the interest in the field has been
increasing, not least due to the pressure to produce more food in a sustainable
manner for a rapidly increasing world population (Goddek et al., 2015; Mageau et al.,
2015). Increasing energy costs and dwindling natural resources such as phosphorous
and water (Sverdrup and Ragnarsdottir, 2014) are forcing the world to take action
and change present-day food production systems. Scientists and innovation
companies have started national and international collaboration projects for
development and future possibilities of local and sustainable food production.
Innovations include aquaponics, production of insects and other products - what
previously would have been thought of as far flung ideas.
One of the main challenges regarding aquaponics and other integrated production
techniques is to join two or more different production systems together. Aquaculture
and horticulture are quite different production technologies and joining them into a
simple aquaponics circulation may result in a stable production system with optimum
output. However, it has hitherto proved to be difficult to join skills, knowledge and
traditions from different production cultures.
Aquaponics in the modern era began in areas that are limited in fresh water,
particularly Australia and other arid regions such as the US Virgin Islands. With limited
fresh water resources and an increasing demand for food to supply a growing
population, these regions began to link fish and plant culture together in an
integrated system. While the Australian movement initially focused on small-scale
food production, the University of the Virgin Island began to trial commercial levels
of production in an attempt to create a viable industry.
2.1 University of Virgin Islands (UVI)
The pioneers in aquaponics include scientists at the University
of Virgin Islands (UVI), led by Dr. Jim Rakocy who began
aquaponics research in the late 1970´s. This system has been
the inspiring layout of several commercial systems in the US
and systems built by several growers and researchers
worldwide. The University of Virgin Islands has been active in
aquaponics research for more than thirty years and has a
globally recognized aquaponics education program. The system developed at UVI is a
raft hydroponic system and the aquaculture part focus is on tilapia production
(Rakocy, 1989; Rakocy and Hargreaves, 1993; Rakocy, 1997; Rakocy et al., 1997;
Rakocy et al., 2003; Rakocy et al., 2004a; Rakocy et al., 2006a; Rakocy et al., 2006b;
Rakocy et al., 2007; Rakocy et al., 2012).
A continuous operation was run at UVI for 2.5 years (1995-1997) with red tilapia and
leaf lettuce production (Rakocy et al., 1997; Rakocy et al., 2007). The system (Figure
2.1) staggered fish production using four fish rearing tanks, each with 7.8 m3 water
volume (total 31.2 m3), two cylindro-conical clarifiers (3.8 m3 each), four rectangular
filter tanks (0.7 m3 each) containing orchard netting, six hydroponic tanks (11.5 m3
each) and a sump (0.6 m3). The hydroponic tanks were 30.5 m long by 1.2 m wide by
0.4 m deep and had a combined surface area of 214 m2. Thus, the surface area to fish
tank volume was 6.85 m2/m3. The water volume was 110 m3. A 0.5 hp in-line pump
moved water at an average rate of 378 L/min from the sump to the fish rearing tanks
(mean retention time of water 1.5 h), from which effluent flowed with gravity
through the system. Air diffusers were used both in fish and hydroponic tanks
through airstones supplied by air from a 1.5 hp blower for fish and 1 hp blower for
The daily fish feed input averaged 12 kg equivalent to 56 g/m2 plant growing area. The
waste water from the fish was only supplemented with potassium (K), calcium (Ca)
and iron (Fe) to provide sufficient amounts of the essential nutrients for normal plant
growth. Potassium and calcium were supplied as hydroxides, also serving to raise the
pH while supplementing these nutrients. These additions were equivalent to 16.1 g
KOH, 3.3 g CaO, 13.7 g Ca(OH)2 (more economical than CaO) and 6.0 g iron chelate
(10%) per kg of fish feed. The annual production of tilapia was 3,096 kg and the
lettuce production was projected to 1,694 cases (appr. 11 tons), or appr. 3.5 tons
lettuce per ton tilapia produced and the land use was 0.04 ha, which can be
considered being a small to medium scale system.
Figure 2.1 UVI aquaponic system diagram (Rakocy et al., 1997)
History of aquaponics
2.2 Developing units in Europe
Aquaponic systems are being developed in several places in most if not all European
countries. Most of the systems are small hobby or research units. In recent years a
few semi-commercial pilot units have been put to the test and these systems provide
excellent information for the future developments.
The SME Breen
in Hondarribia, Spain has developed a
system of 500 m2 during the last five years (Figure 2.2) and is
expanding to a two thousand square meter production
system (Figure 2.3) in Renteria at Tknika
, the Centre for
Investigation and Applied Innovation in VET (Vocational
Education and Training). The installations at Tknika will serve
as the main hatchery of tilapia for production installations, as
research laboratory and as a national and international training facilities in
Breen´s systems have always been run with tilapia production and many different
plants have been tested in the systems, including salads, a variety of herbs,
tomatoes, peppers and oranges. The aquaponics development at Breen started in
2010 and the company has made several test units built on grow-bed, raft and
nutrient film technique (NFT) - see further description of the different systems in
Section 3.4 below.
Figure 2.2 Breen aquaponics pilot unit in Hondarribia, Spain
Figure 2.3 Hatching facilities at Tknika
Figure 2.4 New 6,000 m2 commercial aquaponics farm under construction
Breen has associated with an investor group called NER. This alliance is constructing a
new aquaponics production unit of 6,000 m2 to produce up to 125 tons of tilapia, 15
tons of tomatoes, 6 tons of strawberries and up to 50,000 salads per year. The
installation is situated close to the pilot unit in Hondarribia and is planned to start
operation mid 2016 and be in full production a year later. Photos from the
construction site are shown in Figure 2.4.
Institute of Global Food and Farming (IGFF)
in Denmark has
developed a decoupled aquaponics unit of 60 m2 (Figure 2.5).
The IGFF unit consists of six plant tables arranged in three
pairs of 1.45 x 7.50 m on the top of three rectangular fish
tanks (3 x 1 x 0.8 m) with a usable volume of 2 m3 each. Plant
tables produce horticulture products in pots with soil and
compost to open up for the prospect of getting an organic
certification for the aquaponic system. Soil is used because to obtain an organic
certification requires plants to be grown in various specified types of soil. Silver
Figure 2.5 IGFF aquaponics pilot unit
History of aquaponics
tilapia, red tilapia and pike perch have been tested as fish species and various plants
such as lettuce, basil, tomatoes and peppers have been grown successfully on the
Figure 2.6 shows a schematic drawing of the system. Water to the plants is supplied
by the “ebb and flow” principle. To secure as much as possible plant growing area in
the greenhouse cube, the bio-filter, UV-lighting, air pumps, pH regulation and sedi-
mentation tanks are placed outside the cube (Figure 2.7). The oxygen supply to the
fish tanks is secured by three independent air blowers. The tanks are connected to a
central water discharge line that ends in two sedimentation chambers. These
chambers do not only serve as pre-filtration systems but also as pump sumps. Each
chamber is connected to one separate lift pump, providing a pumping capacity of
around 15m3/h. The total water flow is split into two independent loops. In one of
them, the fish loop, the pumps supply water to a bead filter that acts as a mechanical
as well as a biological filter. This loop has in-line ultraviolet disinfection system (UV
system). From the UV system the water can be led to the plant tables and/or directly
back to the fish tanks located beneath the plant tables. The water from the plant
tables can also enter the fish tanks by gravity or can directly be discharged into the
main discharge line and the sedimentation chambers.
In the second loop (plant loop) the lift pump supplies the water directly back to the
plant tables from where it enters the fish tanks. Both lift pumps are frequency
regulated, and the plant loop pump is equipped with a timer that allows to pre-set
pumping time and -duration to follow a “ebb and flow” watering schedule of the
plant tables (Kledal, 2012).
Figure 2.6 Schematic diagram of the IGFF
aquaponics pilot unit
Figure 2.7 Bio-filter, UV-lighting,
sedimentation tanks and airblower
The Icelandic company Svinna-verkfraedi Ltd
collaboration with the University of Iceland implemented a
RAS system with tilapia in the greenhouses of Akur, an organic
greenhouse horticulture farm in South Iceland. The RAS
system is connected to an NFT system with okra, tomatoes,
beans and lettuce. The fish waste water nutrient solution is
also used for irregation of the organic soil production. The
aquaponic system consists of three 4 m3 fish tanks, a drumfilter, a biofilter, a sump
tank and NFT pipes for larger plants, see Figure 2.8.
Svinna has developed aquaponic systems since 2013 and has run tests with grow
beds, raft and NFT with several other plant types. The setup today is partly decoupled
as part of the water is used for soil irrigation and the plan is to move more in that
direction to secure optimum conditions for both fish and plants. The company is now
adding crayfish to the system to make use of the sludge from the fish tanks.
Furthermore, a worm bed is used for plant waste. Thus, zero-waste is obtained in the
system. The company aims to link educational and experience tourism to the
production showing the water and nutrient cycles, how waste from one production
unit is turned into value for the next one and how sustainable geothermal energy is
used for the production. The future ideas also include a restaurant serving the
products from the system. Moreover, further research is planned for future
development and expansion of production.
Figure 2.8 Svinna aquaponics pilot unit in Laugaras, Iceland
History of aquaponics
(former Bioforsk) in Grimstad South Norway has since
2010 been involved in aquaponics development (Skar, 2010).
The institute developed and implemented a test system in
2013, based on cold water fish and has tested brown trout and
rainbow trout in the RAS system together with salad
production in a raft system, see Figure 2.9. The system has
been running stable with a weekly production of salad. The
system at Nibio includes four 1 m3 fish tanks and two 15 m2 raft basins. Mechanical
filtration is performed at each tank and through a bead filter which also serves as
biofilter. Furthermore, a trickling filter provides additional biofiltration and aeration.
The SME Ponika
in Slovenia has built a 400 m2 commercial
aquaponic system recently starting up production. The system
is situated in the heart of the Landscape Park Goričko and
Natura 2000 site. The RAS system has largemouth bass and the
plants grown are chives, peppermint, basil and lemon grass in
495 rafts, see Figure 2.10.
Figure 2.10 Ponika aquaponics pilot unit in Prekmurje, Slovenia
Figure 2.9 Nibio aquaponics pilot unit in Grimstad, Norway
in Italy has developed a 500 m2 experimental
area under two greenhouses and outdoor space supplied with
floating systems, substrate aquaponics and dynamic root
floating technique (Figure 2.11). The company has successfully
farmed both freshwater (nile tilapia, largemouth bass, African
catfish) and saline fish species (grey mullet, European
seabass). Beside the biological production and the quanti-
qualitative improvement of the productions from traditional horticulture, the focus
of Eureka is to develop new aquaponics solutions for the industry that allow the
expansion of aquaponics with both staples and saline crops. Eureka has been
committed in bringing aquaponics and integrated systems in arid lands, in designing
and running micro systems in South East Asia for food security and to carry out R&D
for the integration of the tilapia nursery industry with aquaponics.
The FishGlassHouse was built at the campus site of the
Faculty of Agricultural and Environmental Sciences (AUF),
University of Rostock in Germany. The fully closed interval
controlled aquaponic system consists of three aquaculture
units (300 m²) and six cabins for plant cultivation under
hydroponic conditions (600 m²). The fish production of
African catfish (Clarias gariepinus) is carried out by using
juveniles from a local fish producer (PAL Anlagenbau
GmbH, Abtshagen). Different plants like herbs and
vegetables are produced within the different hydroponic
subsystems. Experiments are carried out under floating
raft, “ebb and flow”, nutrient flow technique (NFT) or
planting table conditions in cooperation with a local plant
producer, Grönfingers GmbH (Rostock).
Figure 2.11 Eureka farm R&D unit near Rome, Italy
Figure 2.12 FishGlassHouse
History of aquaponics
The University of Applied Sciences (ZHAW)
has conducted research and development of aquaponics for
several years (Graber and Junge, 2009). This has resulted in
the spin-off company UrbanFarmers
and bolt-on aquaponic systems internationally. An aquaponic
research and training facility of 292 m2 has been built at
ZHAW in Waedenswil and a 260 m2 system has been built at
UrbanFarmers in Basel (Graber et al., 2014a; Graber et al., 2014b). This team has been
involved in development of the Aquaponic system in Naklo, Slovenia (Podgrajsek et
in Switzerland operates two tropical
greenhouse sites with coproduction of fish and plants, in
Frutigen with sturgeon and in Wolhusen with tilapia. In both
cases visitor centres are a large part of the business concept
with exhibitions and tours, meeting facilities, shops and
restaurants offering a taste of the products in a tropical
environment. A Tropenhaus facility has also been built in
More European startup companies within aquaponics can be
but in general the systems are still small or in
the designing phase. The EU funded project INAPRO
2018) led by Leibniz Institute of Freshwater Ecology and
Inland Fisheries (IGB) in Berlin, Germany and including 18
partners from 8 countries will implement four large-scale
(each 500 m2) demonstration facilities in Spain, Belgium,
Germany and China.
2.3 Decoupled systems
In recent years recirculating aquaculture system (RAS) technology has been
developing rapidly in Europe. The water reuse in modern RAS can be 95%-99%
(Dalsgaard et al., 2012), with water usage down to below 100 L/kg of fish produced
(Martins et al., 2010). This new technology together with new environmental criteria
for sustainable aquaculture has led to increased interest in aquaponics within
aquaculture businesses. As traditional aquaponics combines fish and plant
production in one simple circulation, and thus the same environment, some
compromise is necessary to obtain optimal growth for the system as a whole unit.
New ideas on decoupled aquaponics involve plans for the physical separation of the
fish and plant subunits in two recirculating loops. This is described as decoupled
systems, where optimal condition for each system is applied with periodic water
exchange between the two subunits. Decoupled aquaponic systems are believed to
provide key steps towards the breakthrough of large-scale commercial aquaponics.
Additionally, decoupled systems offer a level of risk mitigation that a balanced
system does not. In the instance of a fish or a plant pathogen problem, each subunit
can be isolated.
IGFF has constructed the aquaponic pilot unit by having a double loop and thus can
run the system totally or partly decoupled. Figure 2.12 shows photos from IGFF under
Other aquaponic systems such as at Breen, Nibio and Svinna can also run the RAS and
hydroponics part separately by simple adjustments. At Svinna a special nutrient
water tank for the organic plant part growing in soil is using waste water from the
RAS part without returning the water. The hydroponics part could be connected to
this system or a special nutrient water tank collecting waste water from the RAS
system. The nutrient concentrations, pH, temperature etc can then be adjusted for
Figure 2.13 Decoupled system at IGFF
3 System description
3.1 Recirculating aquaculture system (RAS)
Recirculating aquaculture systems (RAS) have gained increasing interest in recent
years as they reduce the water use through circulation and thus use only a small
percentage of water compared to traditional flow through systems. Therefore, the
environmental impact can be minimized while intensifying fish production in a
controlled environment. To maintain good water quality the water has to be filtered
to remove solids, ammonia and CO2. Likewise the dissolved oxygen level, pH and
temperature have to be kept at secure levels at all times. The RAS technology has
been developed in recent years, especially in relation to sludge handling and
biofiltration (Dalsgaard et al., 2012). The RAS technology development, together with
more stringent environmental requirements and the need to increase profitability,
have led to increased interest in integrated multitrophic production methods such as
aquaponics, which converts the RAS water treatment costs for biofiltration into
profit by growing plants that take up nutrients and help to control ammonia from the
fish tanks. A schematic overview of RAS is shown in Figure 3.1.
Figure 3.1 Schematic overview of a recirculating aquaculture system (RAS)
3.2 Mechanical filtration
Fish feed and excrement solid removal is a fundamental step in every RAS in order to
keep good water quality and to prevent the system from failing. Not only does waste
increase the risk of fish disease and gill damage, but also increase the ammonia in the
water, decrease the oxygen concentration due to higher biochemical oxygen
demand (BOD), reduce the biofilter efficiency by fouling the media with
heterotrophic bacteria, and favour clogging that lead to the formation of anaerobic
spots that release hydrogen sulphide, an extremely toxic gas for both fish and
The first goal in solids removal is to reduce the retention time of solids in the system
as much as possible. The sooner solids are separated from the main system, the less
chance there is that solids break down into smaller particles, making them more
difficult to treat, or consume oxygen. Thus, mechanical filters are in general put after
fish tanks and before the biofilter to remove solids originating from uneaten feed and
In aquaponics it is very important to include effective filtering of organic solid. It is
estimated that ineffective solid waste removal has led to more than 85% of failed
aquaponics systems. If the solids are not removed they will have negative impact on
the plants by clogging the roots, and the substrates in media systems which increase
the system oxygen demand and the risk of hydrogen sulphide and methane
generation. Filtration of fish waste water for aquaponics has been found to
significantly increase lettuce yield (Sikawa and Yakupitiyage, 2010).
Dalsgaard and Pedersen (2011) measured all solid and suspended/dissolved waste
from a rainbow trout RAS farm. On average, they found 48% of the ingested N
recovered in the water, total ammonia nitrogen (TAN) constituting 64–79% of this,
and 7% in the solids. In comparison, 1% of the ingested P was recovered in the water
and 43% in the solids. This emphasises the need for using the solid waste as this is a
valuable souce of nutrients. Further research for recovering phosphorus and other
resources from RAS wastes is ongoing (Zhang et al., 2013). Some trials carried out at
the University of the Virgin Islands have proved that composted fish solids are a
valuable substrate for the nursery of plants or for substrate hydroponics due to their
release of mineralized nutrients (Danaher et al., 2011; Pantanella et al., 2011a). The
same team conducted a preliminary evaluation of solids digestion, evaluating the
time it takes for solids to mineralize or release usable dissolved nutrients that were
bound in the discharged solids from their aquaponic system (Rakocy et al., 2005). In
Canada Dr. Nick Savidov‘s research cluster has been focusing on the mineralization of
the fine fraction of solids within the aquaponic system, with the objective of
increasing the nutrients available to plants through increased mineralization.
Mechanical filtration can be accomplished in many ways. Normally filtration methods
rely on gravity (sedimentation, swirl separators/radial flow separators), screening
(microscreen (drum) filter, sand filter, bead filter), oxidation (ozone treatment) or
foam fractionation. It is of great importance to secure operation of mechanical
filtration units at all times and to take care of the sludge that is removed from the
All the different options available have their advantages and disadvantages. A good
overview of basic information is presented in Recirculating Aquaculture by Timmons
and Ebeling (2010) or Aquaculture Engineering by Lekang (2013).
In summary, mechanical filtration techniques relying on gravity require a large
surface area and manual cleaning/purging; they are only efficient at removing large
settleable particles (>100µm) but are generally simple and cheaper to construct.
Filtration techniques relying on screening often require more complicated
equipment, including (automated) backwash features; they can be more expensive
to buy but require much less floor space and are generally self-cleaning.
For sedimentation basins (Figure 3.2 left), radial flow separators and swirl separators
it is important to design the filter in such a way that all turbulence inside the filters is
avoided. Any turbulence, such as sudden change in water velocity will resuspend the
solids and reduce filter efficiency. An additional disadvantage of these filters is that
solids remain in the system´s water, where it promotes growth of heterotrophic
bacteria that can consume large amounts of oxygen.
Drum-filters (Figure 3.2 right) with automatic backwash in contrast will remove solids
within minutes from the system water which allows for separate treatment (e.g.
mineralization/digestion) and reduces oxygen consumption in the system. Drum-
filters require a high-pressure pump for backwash and periodic servicing but are
generally highly automated. Screen sizes between 10µm – 500µm are available but
normally screens in the range of 40µm-80µm are used.
Sand filters have been in use for a long time. Due to the small pore sizes between
grains of sand they provide very good removal efficiencies (down to 5µm) and water
quality. This small pore size also means that a high pressure is needed to pump water
through, generally between 1.5-3 bars. Bead filters require bigger plastic beads which
Figure 3.2 Sedimentation tank (left) and drum filter (right)
cause much less resistance but also a slightly lower filtration efficiency. Good bead
filters (without six-way valves) normally can be run using low-head energy efficient
pumps. Both bead filters and sand filters have the disadvantage that solids are also
kept in the system water until they are purged (manually or automatically) from the
For the removal of fine solids (<30µm) a protein skimmer or foam fractionator might
be used as well. These filters rely on agitation of water to create floating foam to
which fine suspended solids bind and which is then removed from the water via a
foam trap. Foam fractionators are often used in salt water systems but can also be
used in fresh water, albeit with lower efficiency.
The choice between passive sedimentation and mechanical filtration depends on the
degree of intensification of the farm. The smaller the farm and the volume of water
to be treated the more convenient it is to use the sedimentation options due to the
lower costs and lower maintenance, providing that an adequate retention time of
water in the settling tank is maintained. The intensification of production (high fish
stocking densities and higher feed rates), the higher volume of water and the choice
of more sensitive species make the use of drum filters more convenient. The most
important thing is to secure their operation at all times and to take care of the sludge
that has to be promptly removed from the system. Because these filters are so
effective at removing solid waste from the system, they are quickly eliminating
nutrients from the system and plant nutrient deficiencies may appear. Discharged
effluents from the drum filter are thus often digested in a separate loop and
dissolved nutrients returned to the system. Table 3.1 compares the relative cost and
the pros and cons of different mechanical filtering systems.
Table 3.1. Comparison of different mechanical filter systems.
No electricity, requires
only purging the system
Low water volume
compared to alternatives.
Water retention time
depends on the particle
size to be removed.
No electricity, requires
only purging the system
Low water volume
compared to alternatives.
Water retention time
depends on the particle
size to be removed.
limited space for water
treatment. Suitable for
small or medium farms.
Requires electricity, some
beads may need to be
replaced. Water needed
for backflush with
relative disposal. Number
of flushes depend on the
limited space for water
treatment. Suitable for
small or medium farms.
Requires electricity for
pumping, not practical
with organic wastes, as
particles foul on sand
making clogs. More
Effective for big farms.
Water movement is by
Requires electricity, some
screens need to be
Water needed for
backflush with relative
disposal. Number of
flushes depends on the
solid load and the mesh
of the screen.
Biofilters are a prominent feature in recirculating aquaculture and in aquaponic
systems. The water is treated by converting dissolved ammonia, a toxic metabolite
excreted by fish, into harmless nitrate. This conversion, operated by beneficial
bacteria, is the main reason for the huge water saving obtained by RAS, since it
avoids the discharge/replenishment of water normally occurring in traditional
systems to keep ammonia concentrations below toxic limits for fish. A healthy and
matured biofilter is crucial for a stable and well working RAS (Timmons and Ebeling,
2010). There are mainly three nitrifying bacteria species taking part in the conversion:
nitrosomonas convert ammonium to nitrite and nitrobacter and nitrospira convert
nitrite to nitrate. These bacteria are naturally occurring in our environment. They are
very effective aerobic autotrophs using ammonium and nitrites, respectively, as
energy source. However, they need a surface to colonize e.g. gravel, pumice and/or
plastic material. This bacterial substrate needs to have a high surface area.
A biofilter is typically a canister, tank or barrel of some sort that holds a porous
media, bacteria and well aerated water. It can be a very simple setup or industrially
complex. After effective solids removal the water runs through the biofilter where
the ammonium is efficiently converted to nitrite and then to nitrate. The bacteria on
the biofilter are not visible and are not readily measured outside of laboratory
conditions. Therefore, the best way to determine whether it is working is to
constantly monitor the levels of ammonium, nitrite and nitrate.
An acclimation period is required to start up any new system. During this time of
beneficial bacterial establishment operators must monitor ammonia and nitrite
closely to avoid lethal levels. Each fish species has unique tolerances to these
parameters. The startup of a new biofilter can take as long as six weeks depending
on environmental conditions (e.g. temperature, dissolved oxygen, pH or salinity).
Initially ammonia levels will rise until the nitrosomonas bacteria colonize the system.
At this time ammonia will begin to decline. As ammonia declines it is converted to
nitrite and a corresponding rise in nitrite levels will be observed. Once the
nitrobacter/nitrospira bacteria have established, nitrite levels will decline resulting in
production of nitrates. Once nitrates are produced and ammonia and nitrite levels
remain low the system can be considered acclimated and ready to feed at maximum
capacity of the designed system. There are methods of speeding up the acclimation
of a new system including dosing the system with ammonia before fish are
introduced, then monitoring for the trends in ammonia, nitrite and nitrate. Another
method is to seed or inoculate a new system with cultured water from an already
Nitrate is relatively harmless to the fish and is the primary nitrogen source for the
plants. From the overall chemical processes shown below, it can be noticed that
hydrogen ions are released meaning that the pH of the system will be lowered,
depending on the buffer capacity of the system. The progressive consumption of
alkalinity due to the continued release of hydrogen ions needs to be properly
balanced by the constant supply of bases in the form of carbonate ions (calcium
carbonate), bicarbonate ions, or alkali (calcium hydroxide, potassium hydroxide). It
should also be noted by the equations below that the nitrification process is also
oxygen consumptive. The beneficial bacteria rely on a constant supply of oxygen to
Nitrosomonas converting ammonium to nitrites:
NH4+ + 1.5 O2 → NO2- + 2 H+ + H2O
Nitrospira/Nitrobacter converting nitrites to nitrates:
NO2- + 0.5 O2 → NO3-
The overall reaction for ammonium conversion to nitrates is:
NH4+ + 2 O2 → NO3- + 2 H+ + H2O
RAS is a dynamic system, fish are constantly producing ammonia and excreting it into
the water. Ammonia is transported into the biofilter and converted into nitrate. In a
healthy system the concentration of ammonia is always within non-toxic levels for
the fish. Nitrite, the product of the first step of ammonium conversion, is also toxic to
fish. Hence, both bacterial colonies must be fully functioning.
The size of the biofilter depends on several factors (Chen et al., 2006). Those are:
Oxygen concentration in water
Surface area of filtration media
Water exchange rate in the biofilter tank
Fish stocking density and feeding regime
Protein content of the feed
Many biofilter options exist and performances depend on the technology and the
characteristics of the media. Common biofilters in use are (see Figure 3.3):
Bead filters - biofilter media is contained in a pressurized chamber. Beads are
periodically stirred to clean the media from accumulating dirt that is
removed through backflush.
Sand filters - the media is contained in a pressurized chamber and is agitated.
The higher specific surface of sand allows for very high nitrification rates.
Trickling filters - can be used with different media having various specific
surfaces such as plastic beads, gravel or clayballs. Water is sprinkled on top
of the canister allowing nitrifying bacteria to grow on the water-air interface
of the media. Trickling filters provide a passive aeration and carbon dioxide
Moving bed bioreactors (MBBR) - neutrally buoyant beads or biomedia are
kept agitated in water by means of aeration or stirring. Aeration keeps water
oxygenated and removes carbon dioxide from water.
In aquaponics the use of media beds for the plants bring additional biofiltration
capacity, which make the systems more resilent to ammonia peaks.
Figure 3.3 Bead filter, trickling filter, moving bed bioreactor and swirl separator
Beside the passive aeration occurring in biofilters water needs to be adequately and
constantly aerated to provide sufficient oxygen for plants, fish and the microbial
community. The amount of oxygen required depends on the species being reared, on
the fish density and the feed supplied to the animals.
Hydroponics is a soil-less horticulture method of growing agricultural crops. Various
substrates provide plant support and moisture retention. Within these media
options, irrigation systems are integrated, providing a nutrient-rich solution to the
root zones. All the necessary nutrients for plant growth are supplied by this solution.
There are several designs of hydroponic systems, that might serve different
purposes, but all have those mentioned basic characteristics.
Aquaponics uses the system design of hydroponics for growing plants. There are
three main aquaponics techniques widely in use worldwide; media beds, floating
rafts or deep water culture (DWC) and nutrient film technique (NFT), see Figure 3.4.
The media beds utilize various substrates in an “ebb and flow” process while in the
NFT (in thin layer of water) and raft/DWC systems (floating rafts in large water tanks)
the plant roots grow directly into the water.
These systems can all work well, nevertheless they all require effective mechanical
filtering to avoid fish waste accumulation on the plant roots. In small scale
aquaponics the media-based systems are often used for both mechanical
filtration/solid removal and biofiltration. This may work well for very low stocking
densities (below 10 kg/m3) or with feeding regimes of 15-20 g/m2/day. Organic waste
tends to accumulate if these systems are not properly managed and they eventually
need to be cleaned to maintain a healthy environment for both fish and plants. In
these lightly fed systems, worms are often introduced to the media bed to process
solids that may otherwise accumulate leading to anaerobic zones within the bed. NFT
and DWC systems are convenient for smaller plants as salad, greens and herbs and
can be used for larger plants as well. The NFT system is probably the easiest system
to operate in large commercial scale operations, especially for leafy vegetables with a
fast turnover, as it is easier to handle and to clean the system between batches and it
requires much less water pumping. Lennard and Leonard (2006) did comparison
tests on media bed, raft (DWC) and NFT for lettuce production in aquaponic systems
and the results showed significant less growth in NFT. On the other hand successive
studies carried out in Italy showed that NFT performed as well as DWC providing that
adequate nutrients levels and water flow are maintained in the troughs (Pantanella
et al. 2012).
Figure 3.4 From left: Media bed, nutrient film and floating raft aquaponics
3.4.1 Grow beds
Grow beds (Figure 3.5) are often used in different
backyard aquaponic systems and are perhaps the
simplest and most used technique for small scale
systems. It is a solid media-filled bed system,
filled with e.g. gravel, expanded clay or pumice
that provide additional surface for
biofiltration/nitrification, mineralization and thus
efficient plant growth. Grow beds simplify the
management tasks for unexperienced
aquaponists because the additional nitrification
occurring in the media reduce the risks of
ammonia peaks due to fish overstocking or
overfeeding. The grow bed is periodically flooded
and drained with water from the aquaculture. The “ebb and flow” of water and air
allows the media to “breath” and to meet the needs of nitrifying and heterotrophic
bacteria that use oxygen, water and dissolved wastes to mineralize and free
nutrients for plants. Media bed systems are often used to remove solids under very
low fish stocking densities. For long-term operations, higher fish densities and
feeding regimes, a dedicated solid removal unit is needed. If the fish to plant ratios
are too high thus bringing amount of wastes above the bacterial capacity to
mineralize them, the grow beds start to accumulate organic matter and can
eventually clog leading to toxic anaerobic conditions followed by the production of
hydrogen sulphide and methane, which can kill both fish and plants. Nitrifying and
heterotrophic bacteria are a vital part of the grow bed, moreover, worms can be
added to enhance the break-down of organic materials (vermi-compost). The grow
bed is excellent for fruity plants such as tomatoes and cucumbers, due to the
mechanical support provided for the roots of the plants but can also work well with
strawberries and leafy vegetables.
3.4.2 Nutrient film technique (NFT)
The nutrient film technique (NFT) system (Figure
3.6) is based on growing plants in long narrow
plastic channels with a thin film of water
continuously flowing through. The NFT system
needs good preliminary mechanical filtering
systems, as accumulation of solids on the roots
needs to be avoided. An aquaponic NFT system
mainly follows the same technique of
hydroponics, with preferably flat-bottomed
channels positioned at 1% slope and a water flow
Figure 3.6 Nutrient film technique
with okra plants
Figure 3.5 Grow-beds at Breen
regime of 1-2 L/min. Given the small volume of water channels must not be longer
than ten meters to avoid oxygen depletion by the roots. NFT systems are suitable for
smaller plants such as salad and herbs and may even be used for larger plants
including tomatoes and okra. NFT is a popular option for small hobby systems and
good looking show cases. They are also excellent for large scale production units. The
pipes are easy to maintain and clean between batches and the system requires much
less energy for pumping very small volumes of water if compared with DWC and
grow bed systems. Nonetheless, there are issues with NFT systems such as the
decrease of the water‘s nutrient content towards the pipe‘s outlet. This can be
solved by increasing the flow of nutrients delivered into the pipe. Root clogging and
potential high temperature nutrient solutions can also result using NFT. Extra
precautions should be taken to ensure a reliable source of backup power. Without
water-flow roots can quickly dry out killing plants.
3.4.3 Raft / deep water culture (DWC)
The raft system also known as deep-water
culture (DWC) (Figure 3.7) is used for small as
well as large aquaponic systems. Tanks are in
general 30 cm deep filled with water and with
plants floating on plastic sheets accessing the
water through openings. The plant´s roots grow
directly into the oxygenated water continuously
flowing from and to the fish tanks with a
volumetric exchange rate of approximately 30%
per hour. The leaf crop management typically
consists in the transplanting of 3-week old
seedlings growing on media cubes in each of the
openings of the raft, at one end of the tank. The
plants are then harvested at the other end of the tank following a conveyor
movement of the rafts that are movable on the water. This provides a space-efficient
and productive system ideal for large scale systems. The DWC is very stable as plants
can withstand temporary power outages due to the consistent volume of water
available containing both oxygen and nutrients. This technique shows some
challenges in providing a stable and clean system due to organic sediments (fish
wastes, crop wastes, biofloc precipitates) settling at the bottom, which require an
efficient mechanical filtering to process fine particles in an optimal way. Lack of
proper solid waste management would result in sludge accumulation on the plant
roots, starving them from oxygen and the uptake of N-nutrients.
Figure 3.7 Floating system / deep
water culture (DWC)
4 System control and optimization
Maintaining good water quality within aquaponic systems is fundamental to the well-
being, sustainability and success of the system. Water quality is a broad term
encompassing anything that adversely affects the conditions required for
maintaining healthy fish and plants. Therefore, requirements for maintaining water
quality can vary in different parts of the aquaponic systems. It is necessary to
understand the water conditions required in each part of the system and how they
affect other parts of the aquaponic system so that these parameters can be
monitored and adjusted when necessary to maintain a well-balanced system. For
large scale aquaponics it is necessary to maintain a healthy environment for fish,
plants and bacteria continuously to obtain good quality and optimal production from
each sector. Thus, it is necessary to implement good management practices and
system control, including automatization and necessary alarms. The main parameters
and their control are described in the following Section.
4.1 Controlling environmental parameters
The water in aquaponics is the life-blood of the system. It is the liquid medium
through which all essential macro- and micronutrients are transported from the
aquaculture to the hydroponics component of the system, and the medium through
which both the fish and plants receive oxygen. Thus, water is one of the most
important medium to understand in an aquaponic system. There are plenty of
parameters involved, but five key water quality parameters are of special importance
to follow closely and even with online monitoring: dissolved oxygen (DO), water
acidity (pH), water temperature, nitrogen compounds and electrical conductivity (EC)
of the water. Each parameter has an impact on the unit’s organisms i.e. fish, plants
and bacteria. Each organism has an ideal parameter range for optimal growth.
Other water parameters are necessary as well but can be measured once a week or
even once a month or more seldom in well balanced and stable aquaponic systems.
These include phosphorus and other macro- and micronutrients, carbon dioxide and
total dissolved solids.
On-line monitoring of temperature, pH, ammonia, DO and EC can be undertaken by
simple and relatively inexpensive aquarium control systems e.g. from Profilux or
more expensive industrial equipment e.g. from Hach, Oxyguard or Priva, related to
the size and design of the system. Aquarium kits for measuring e.g.
ammonia/ammonium, nitrite, nitrate and phosphate are quite accurate and cost
efficient. For more accurate measurements spectrophotometers such as from Hach
or Hanna Instriuments or portable multifunction probes can be used for most
System control and optimization
Each fish species and plant type has a preferred temperature range that should be
researched for optimum fish growth, bacterial activity and plant production.
Generally, tropical fish thrive at 22–32°C while cold water fish prefer 10–18°C. With
respect to Oreochromis niloticus (Nile tilapia) their vital range lays between 14-36°C
(they do not feed or grow below 17°C, and die below 12°C) and the optimal growth
range is between 27-30°C. The latter allows the best growing performance; i.e. a
grow-out stage of 600-800 grams in 6 - 8 months (Timmons and Ebeling, 2010).
Additionally, optimal temperatures (and consequently less stress) reduce the risk of
diseases. Thermal isolation, heat exchangers, water heaters and coolers help to
achieve a steady temperature level, however, these means may be costly in areas
and/or countries where energy/electricity is expensive. It is thus often better to grow
fish adapted to local environmental conditions. Plants also have different
temperature requirements, e.g. 15-19°C for salads while tropical plants need higher
temperature and humidity.
The acceptable temperature range for nitrifying bacteria is 17–34°C. This range
encourages growth and productivity. In particular, the Nitrobacter group is less
tolerant with respect to lower temperature compared to the Nitrosomonas group,
and as such, during colder periods nitrite should be more carefully monitored to
avoid harmful accumulations.
4.3 Dissolved oxygen
Oxygen is essential to the survival of fish in all aquatic systems. The solubility of
oxygen decreases with rising water temperature and increasing salinity. Oxygen is
measured as dissolved oxygen (DO) and it is possibly the most important water
quality parameter in an aquaponic system. To obtain good fish growth, DO levels
should be maintained at saturation and at least above 5 mg/L. Low dissolved oxygen
levels are responsible for more fish kills in aquaculture, either directly or indirectly,
than all other problems combined (Lennard, 2012). Oxygen consumption is directly
linked to size, feeding rate, activity level, system cleanliness from wastes and
temperature; large fish consume less oxygen than their smaller counterparts, which
have higher metabolic rates. Warm water species, e.g. tilapia, may better adapt to
the occasional low DO levels than cold water species. All species can tolerate adverse
condition for short periods, provided that such occurrences are infrequent. Low DO
Cold water fish
can though cause potentially irreversable damage to gills and reduce the efficiency of
the nitrifying bacteria.
4.4 Chemical oxygen demand and biochemical oxygen demand
The chemical oxygen demand (COD) and the biochemical oxygen demand (BOD) are
measures of the amount of organic matter in the system that use up dissolved
oxygen, therefore, high CODs and BODs are not desirable, especially for fish health.
Both of these parameters are measured using laboratory methods and performed
less frequently e.g. once, or a few times a year. COD and BOD can be kept low by
maintaining effective filtering of solids in the system and regular cleaning of tanks
Water acidity (pH) is known as the master variable in aquaponics because it
influences many water quality parameters, including % NH3 vs. % NH4+ available as well
as the solubility of other plant nutrients which affects both fish and plants. As a
measure of acidity, pH is presented on a logarithmic scale from 0-14 where pH 0<7 is
acidic, 7 is neutral, and 7<14 is basic. The pH of a water system represents the amount
of hydrogen ions - also referred to as a measure of the hydrogen ion activity (H+) of
pH = - log (H+)
The equation shows that as the hydrogen ion activity rises, the pH is lowered. This
means that acid waters have high levers of H+ and hence low pH.
Temperature and pH affect the total ammonia nitrogen (TAN) of the water: e.g. at
pH 4.5 nitrification has ceased and TAN concentrations increase.
The acceptable range for fish culture is usually between pH 6.5 to pH 9.0. When
water is very alkaline (>pH 9), ammonium in water is converted to toxic ammonia,
which can kill fish, on the other hand, acidic water (<pH 5) leeches metals from rocks
and sediments (and solid substrates in grow beds). These metals have an adverse
effect on the fishes’ metabolism rates and ability to take in water through their gills,
and can be fatal as well. Aquaculture pH guidelines for warm water fish suggest that:
pH<4.0 is acid death point; pH 4.0 – 5.0 there is no production, pH 6.5 - 9.0 is a
desirable range for fish production, pH 9.0 - 11.0 gives slow growth, and pH> 11.0 is
the alkaline death point (Lawson, 1995; Tarazona and Munoz, 1995). Importantly,
System control and optimization
different fish species can be more tolerant to changes in pH. For example, tilapia can
tolerate a wider pH range, pH 5.0-10.0, but other species may not.
Plants prefer pH< 6.5 and nitrifying bacteria perform optimally at pH> 7.5. Usually pH
is one of the water quality parameters that the optimum value for fish does not
match with the optimum pH for plant growth
(Rakocy et al., 2004a). This remains one of the
challenges of the simple aquaponic systems: to
balance the fish pH to the particular plant pH
requirements. Based on these data the highest
possible pH value should be consistent with the
prevention of toxic NH3 accumulation in the
aquaponic system. Consequently the ideal pH
value for the system ranges often between pH
6.8 and pH 7.0. Bases such as calcium carbonate,
calcium hydroxide and potassium hydroxide may
be added to increase pH and maintain pH close
to neutral (pH 7.0).
The pH level needs to be monitored frequently: at least once per week or more
frequently. Daily monitoring is suggested as pH generally declines on a time scale of
one day as a result of nitrification and respiration. There are several online systems
designed for continuous monitoring of pH.
Nitrification produces weak concentrations of nitric acid due to the release of
hydrogen ions during the oxidation of ammonia to nitrate. This continuous release
brings the aquaponic system to progressively consume alkalinity and become acidic.
Fish respiration increases CO2 levels in the water, which leads to lowering of pH. CO2
is also a product of the nitrification, since 5.02 g of carbon dioxide are formed per
each gram of ammonia nitrogen. CO2 build-up in diffuse aeration systems is less
frequent as it vent off to the atmosphere. Also, CO2 levels should not exceed 20 mg/L
because at higher levels the fish become sluggish and cannot absorb enough oxygen
through their gills.
Alkalinity is linked to pH. Alkalinity as CaCO3 equivalents is the sum of the carbonate
(CO32-) and bicarbonate (HCO3-) ion equivalents. It represents the ability of a water
system to neutralize acid in the water without changing its overall pH level. Alkalinity
is a key parameter that should be measured once per week to once per month,
depending on the size of the aquaponic system and fish stocking density. Maintaining
alkalinity >100 mg/L as CaCO3 is recommended. The correct pH, alkalinity and
hardness (high content of dissolved ions - sometimes referred to as high mineral
content) are known to be essential for a successful pond fertility aquaculture
Great care must be taken when
adding base to the system as a
large amount of base in a single
dose will shift the majority of
TAN into the toxic form (NH3)
and kill all the fish. It is therefore
recommended to add base very
slowly over a period of several
programme. Alternately adding calcium carbonate, calcium hydroxide and potassium
hydroxide from a base addition tank is suggested for correcting pH when it is
dropping (towards acidic). Hydrogen ions from nitrification are neutralized by
hydroxides (OH-) from completely dissociated strong alkali, or react with the
carbonate or bicarbonate ions to form carbonic acid (H2CO3) which is a weak acid.
This results in the pH increasing once more towards a more neutral pH. The buffering
capacity in intensively run RAS and aquaponic systems is quite high, because each
gram of ammonia nitrogen consumes 7.02 grams of alkalinity (as CaCO3) during the
In summary alkalinity is the sum total of components in the water that tend to
elevate the pH of the water above a value of about 4.5. It is measured by titration
with standardized acid to a pH value of about 4.5 and it is expressed commonly as
milligrams per liter of calcium carbonate. Alkalinity, therefore, is a measure of the
buffering capacity of the water, and since pH has a direct effect on organisms as well
as an indirect effect on the toxicity of certain other pollutants in the water, the
buffering capacity is imperative for water quality. As stated above carbonates and
bicarbonates, which commonly occur in natural waters, increase the alkalinity. Also
affecting the alkalinity are phosphates and hydroxides.
4.7 Nitrogen compounds
Nitrogen is one of the critical water parameters. It is part of all proteins and is
required by all known life species. Nitrogen enters the system from the fish
excrement – and thus indirectly from the feed. A typical protein content in feed for
tilapia is 30-32%; whereas carnivore cold water species require a higher protein
percentage appr. 50% (Jokumsen and Svendsen, 2010). The proteins result in fish
growth and have a high impact on the feed conversion ratio (FCR), the remainder is
released as solid and liquid fish waste (Timmons and Ebeling, 2010). The liquid fish
waste is mainly released via the gills or the fish’s urine in form of ammonium (NH3 or
NH4+, depending on the pH of the system). The solid waste that is released into the
water in the form of fish excrements (faeces) or uneaten feed, are converted into
ammonium by microbes. The extent of this conversion depends on the system design
and the degree of microbial activity. NH3 and NH4+ are then nitrified by the bacteria,
as explained in the biofiltration Section 3.3 above and in Figure 4.1. The sum of
nitrogen from NH3 or NH4+ is called total ammonium nitrogen (TAN). It is
recommended to keep TAN as low as possible and below 3 mg/L. Ammonia (NH3),
which is the unionized form of TAN mainly occurring at high pH, is toxic to tilapia at 1
mg/L. Nitrite is toxic to tilapia at 5 mg/L and should also be kept as low as possible.
Although ammonia and nitrite (NO2-) are approximately 100 times more toxic to fish
than nitrate (NO3-), the latter can also be harmful to fish at specific concentrations.
These depend on the fish species used and the duration they are exposed to the
respective concentration. Tilapia is in general a hardy fish and it can easily widthstand
System control and optimization
concentrations of 100 mg/L or more. All four forms of nitrogen (NH3, NH4+, NO2-, NO3-)
can be used by plants and stimulate growth (Seawright et al., 1998) however the
form quickly absorbed by plants is nitrate.
The frequency of measurement should be weekly to monthly for nitrate and nitrite
(more frequent if there are problems in supplying DO), but monitoring of TAN should
occur on a weekly basis, or more often depending on the environmental conditions,
feeding regime and the fish stocking density.
Nitrate is the common form of combined
N found in oxygenated waters and can
be biochemically reduced to nitrite,
which can be rapidly oxidised to nitrate
once more (denitrification (nitrate
reduction) / nitrification (oxidation of
ammonia or ammonium to nitrite)).
Natural concentrations of nitrates in
rivers are usually less than 0.1 mg/L but
may be enhanced by anthropogenic
sources. Nitrate and nitrite concen-
trations typically range between 0–20
mg/L N (Robards et al., 1994) and 1-100
µg/L N (Chapman, 1998), respectively.
However, in cases of extreme pollution,
concentrations may be as high as 1 mg/L
NO2-N such as in waters strongly influenced by industrial effluent, or 500 mg/L NO3-N
in areas of high N fertilizer application (Chapman, 1998).
The possibility of overfertilization/overnitrification of waters leading to algal blooms
can occur, if nutrient such as nitrate and phosphate are high. This is termed
eutrophication and refers to the enrichment of waters by inorganic plant nutrients
which results in the stimulation of an array of symptomatic changes. The most
common effects are reduced DO levels because of the high BOD of these blooms,
leading to mortality of the fish/aquatic life. These consequences are far-reaching and
can compromise ecological, social and economic functions of the involved
waterbodies (Chapman, 1998; Smith et al., 1999; Withers and Muscutt, 1996).
4.8 Electrical conductivity
Another very important characteristic of the nutrient solution used in hydroponics is
the electrical conductivity (EC) measuring the concentration of total dissolved solids.
The EC is easy to measure and a good guide, nonetheless, it should be noted that EC
can be lower in aquaponic systems compared to numbers given in hydroponics
Figure 4.1 Schematic representation of the N
cycle in aquatic system
4.9 Macro- and micronutrients
Plants within the aquaponic system need several nutrients that are required for the
enzymes that facilitate photosynthesis for both growth and reproduction. Usually,
these nutrients can be taken up from soil. As hydroponics is a soil-less cultivation
method, these nutrients have to be supplied in another way. Just like the total
nitrogen, these nutrients come through the fish food as fish waste. The nutrients are
split up into two categories; macro- and micronutrients. Whereas the six
macronutrients are way more essential for plants, micronutrients should also be
taken into consideration, although they are only needed in trace amounts. Jones et
al. (2013) outline that there are six macronutrients: Nitrogen (N), phosphorous (P),
potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S). The range of
micronutrients is much bigger. Iron (Fe) is often added to aquaponics due to its
general deficiency in those systems. Other important micronutrients include copper
(Cu), boron (B), manganese (Mn), molybdenum (Mo) and zinc (Zn). The reader is
advised to consult dedicated references or manuals on plant nutrition or hydroponics
to deepen his/her knowledge on plant nutrients, for eample
Nitrogen (N) is primarily the basis for all proteins, as mentioned above. That is why
nitrogen is a key element in aquaponic systems. Nitrogen needs are particularly high
during plant’s vegetative growth (young stages) and before fructification, but are
reduced during maturity to avoid difficulties to blooming, fall of young fruits and
lower quality of produce. Excess of nitrogen fertilization makes also plants more
prone to pests and diseases, due to the ternderness of the vegetable tissues.
Nitrogen deficiencies are very obvious; the yellowing of older leaves is a main
indicator that the system lacks N. In plants, nitrogen can be reallocated within plant
tissues because it is a mobile element. In case of N deficiency, N gets transferred
from older leaves to new growth areas, which is the reason why N deficiency can be
mainly observed in old leaves.
Phosphorous (P) is essential for the plants‘ DNA, phospholipid membranes, and as
adenosine triphosphate (ATP). The latter can also be found in human muscles and is a
component to store energy in cells. It is particularly required in young tissues.
Phosphorus is essential for both photosynthesis and the formation of sugars and oils.
Deficiencies can lead to poor root growth as energy cannot be transported through
the plant in a proper way. Its insufficient supply causes also reddening of leaves due
to antocianins or stunted growth with dark green leaves and delayed maturity. Tips
of leaves might also appear burnt.
System control and optimization
Potassium (K) is mainly involved in flower and fruit
setting with the role of cell signalling via
controlled iron flow through the plants‘
membranes. It is an enzymatic activator and
supports the synthesis of proteins, carbohydrates
and starch. It is also responsible for the
transportation of glucose, water uptake and
desease resistance. Indicators for a deficiency of
potassium can be burned spots on older leaves or
bad plant vigour. Also, flowers and fruits might
abort or not develop properly. Being one of the
limiting elements of aquaponic systems it is
important to constantly supply potassium into the
system, expecially if fruiting plants are grown. Figure 4.2 shows evidence of
potassium deficiency in a tomato plant.
Calcium (Ca) is essential for cell walls and
membranes. It has a high impact on the strength
and development of stems and roots. Calcium
deficiencies are very common in aquaponics. Tip
burn of lettuces and blossom end rot of fruity
plants can indicate that there is a deficiency of Ca
in the system. Figure 4.3 shows how calcium
deficiency can affect the tomato growth. The
issue is that Ca only can be transported through
active xylem transpiration, which occurs when
the plants are transpiring. A proper ventilation to
avoid a high humidity can mostly solve the
problem. Calcium is one of the limiting elements
in aquaponics. Calcium carbonate or calcium hydroxide supplements can be added to
the system to increase the pH buffer capacity.
Magnesium (Mg) is a key element in photosynthesis and plant metabolism and is at
the core of every chlorophyll molecule. Deficiencies are hardly found in aquaponic
systems, but could be spotted if the area between the veins of old leaves turns
Sulphur (S) is important with respect to the production of proteins. Deficiencies are
rare, but can be spotted in young leaves that turn yellow, stiff and brittle, and finally
Figure 4.3 Calcium deficiency
affecting tomato production
Figure 4.2 Potassium deficiency in a
Iron (Fe) is a micronutrient that is used in
chloroplasts and the electron transport chain. It is
critical for photosynthesis and deficiencies are
often found in aquaponic systems since it is a
limiting element. If there is lack of Fe, all young
leaves and vegetative tips turn yellow, or
eventually white with necrotic patches all over
them. As iron (just like calcium) is a non-movable
element, its deficiency can be easily identified
when new leaves appear to be chlorotic while old
leaves remain green. Iron has to be added into the
system up to concentrations of 2 ppm. Iron is
normally added in its chelated form, which makes
this element easily available to plants. Given the susceptibility to pH it is important to
keep the pH below 8 to avoid iron from precipitating and becoming insoluble. The
rule of thumb is to add 5 ml of iron per 1 m² of plant cultivation area. Too high
concentrations of iron do not harm the system but might give a reddish colour to the
water. Figure 4.4 shows iron deficiency in an okra plant.
Figure 4.4 Iron deficiency in an okra
5 Production management
Aquaponics is a sustainable way to grow vegetables and other plants, as the effluent
from aquaculture is used as nutrient solution for hydroponic plant production. To
obtain and maintain balance in the system and secure optimal crops – the production
of fish and plants, respectively has to be kept stable and the environmental
parameters need be controlled as discussed in Section 4. The main production
parameters are air temperature, water temperature, concentration of macro- and
micronutrients, dissolved oxygen in air and water, CO2 in air and water, pH, and light.
These key parameters should be set to meet the optimal requirements of the fish and
plant species being cultivated. The smaller the gap the more productive the system
is. In temperate areas spring-fall crops would particularly fit cold water fish species.
On the contrary warm seasons would favour warm water fish species and
macrothermal plants such as tomato, cucumber and basil.
Climatic control in greenhouses can easily extend the growing season and allow
farmers to produce throghought the year. However higher costs for heating and
lighting need to carefully target the market prices for off-season products in order to
have a chance to make profits.
Other factors of importance are to prevent insects, diseases and other source of
pollution to the system. Aquaponics is less prone to diseases compared to
hydroponics, where sterile conditions in substrates are maintained in lieu of heavily
colonized habitats with beneficial microorganism. Nevertheless traditional
aquaponics have less options than traditional organic agriculture in the use of
biological compounds, which could, in some cases, be toxic to fish. In the case of
pests the physical exclusion through insect-proof nets and the use of beneficial
organisms (predators/parasitoids, insecticidial soaps, biological organisms) are highly
effective in maintaining good crops. On the other hand, the possibility to decouple
aquaponics into two quasi-indipendent systems (fish and plants) that are occasionally
joined together would bring additional options in terms of organic pest and disease
On the nutrition point of wiew, the following of simple plant/fish ratios would ease
the management of the nutrient pool, providing that limiting nutrients, such as
calcium, phosphorus and iron are constantly supplied, also through buffering.
According to mass balance calculations the plant biomass should be 7-10 times the
fish biomass based on a feed conversion ratio (FCR) of 1. In practice 4 kg of plants to 1
kg of fish is often observed. Nevertheless a simpler rule of thumb is to use, on
average, 40-50 g/m2/day of medium protein feed (32% crude protein) for leafy
vegetables and 50-80 g/m2/day for fruit vegetables.
Fish management requires the maintenance of optimal growth conditions for the
species being cultured. Good environment and dedicated stress management would
sensitively increase the fish performance and reduce mortality. The choice of fish
should take into account the local market demand and the profitability, but at the
same time the capacity of the system to maintain optimal environmental conditions
in order to keep costs under control. Performances of fish in aquaponics vary greatly
among species, the fish growth stages, and the quality of feed used. Yet it is not
uncommon to obtain FCR of 1.0-1.2 up to 1.6.
5.1 Choices of species – fish
Most aquaponic systems have been running with
Nile tilapia (Oreochromis niloticus) (Figure 5.1), as
the main fish species. Tilapia is a tolerant warm
water species and therefore a popular fish in
aquaponic systems. Tilapia grows fast given the
right conditions and may achieve approximately 1
kg in 8-9 months. However, the quality of water
and feed will affect the growth (Martins et al.,
2009). The optimum temperature is 27-28°C and
the feed should contain about 30% protein.
Tilapia is easy to breed, grows fast, tolerates a
wide range of environmental conditions and has
a nice white flesh of good quality. The market price is relatively high for good quality
products. Tilapia is today the most popular farmed white fish in the world, and due to
its fast growth it is often known as the aquatic chicken.
Rainbow trout (Onchorhynchus mykiss) has gathered increased interest in recent
years for aquaponics in the Nordic countries where it is widely grown in aquaculture,
Over the past years tilapia has been largely used in aquaponics
with interesting growth rates given optimal environmental
conditions, water quality and feed. Performances on feed
conversion ratio range within 1.1-1.8 (Seawright et al., 1998;
Watten and Buschs, 1984; Tyson et al., 2008; Rakocy et al.,
2004b), whilst recirculating tank systems show values of 1.4-1.8
(DeLong et al., 2009) and cage culture/earthen ponds can range
from 0.82-0.98 (Ying and Lin, 2001) up to 1.2-1.5 (El Sayed, 2006).
Likewise the fish growth rate, measured as specific growth rate
(SGR: % of daily body weight increase), can be 0.91% - 5.1% in
aquaponics (Seawright et al., 1998; Al-Hafedh et al., 2008), while
recirculating tank systems show values of 1.4-1.8 (DeLong et al.,
2009) and cage culture/earthen ponds can range from 0.82-0.98
(Ying and Lin, 2001) up to 1.2-1.5 (El Sayed, 2006).
Figure 5.1 Nile Tilapia
not least in Denmark being the most dominant species in Danish aquaculture
(Jokumsen and Svendsen, 2010). Rainbow trout is a cold water species tolerating
temperature up to 20°C and with optimum rearing temperature of 17-18°C. This
complies well with the optimal temperature in salad production of 15-19°C. A
temperature control would be needed to secure water temperatures below 20°C at
all times, as higher temperatures will stress the fish and even kill it. On average it
takes 7-8 months to grow rainbow trout from 20 g to 300 g (portion size) in RAS in
Denmark (Dalsgaard et al., 2012) and the protein content needed in feed for good
growth is 45-50% and higher for juveniles. The researchers at Nibio in Grimstad,
Norway have carried out studies in aquaponics based on rainbow trout and salad
production with good results providing excellent quality and good growth rates.
Developments in RAS have resulted in effective model trout farms with fish density
of approximately 50 kg/m3, a water of maximum 0.15 l/sec/ton feed/year or 3,600 l
per kg produced fish with a FCR close to 1.0. This is 15-25 times lower water
consumption than in traditional flow-through fish farms (Jokumsen and Svendsen,
2010). Today the waste water is drained to so-called plant lagoons for cleaning. The
plants themselves are not used as commercial products, and thus it is seen as a
natural step further to add plant production systems to the RAS systems and turning
these into aquaponics. Further information about farming rainbow trout in RAS can
be found in dedicated literature (Jokumsen and Svendsen, 2010; Dalsgaard et al.,
Table 5.1. Water quality parameters observed under general conditions in operating,
commercial or pilot scale RAS (Daalsgaard et al., 2012)
Aquaponics can be run with a wide range of fish but in all cases the environmental
criteria has to be met for the chosen species. Table 5.1 compares water quality
parameters for different species in RAS. On a qualitative point of view RAS and
aquaponics proved that the fish containment helps to prevent any risks of parasites
or chemical pollution from external water sources. On the other hand the rearing of
fish in closed systems has proven no risks of heavy metal build-ups in fish meat
compared to the levels found in animals reared with traditional systems (Martins et
5.2 Choices of species – plants
Plants in an aquaponic system need to have good environmental conditions for good
and healthy growth. They require optimum conditions in comparison to, light,
oxygen, carbon dioxide, pH, temperature and nutrients, which eventually secure fast
and healthy growth against pests and diseases. Several crops have been produced in
aquaponic systems and many of them have performed very well. The soilless plant
production starts by seed, cuttings or by transplants.
Other fish also have shown interesting perfomances in aqua-
ponics if compared against RAS. In the case of young African
catfish SGR from aquaponics (1.36% - 2.13%) (Endut et al., 2010;
Pantanella et al., 2011a) is similar to recirculating systems (1.24% –
1.94%) (Pantazis and Neofitou, 2002; Ahmad, 2008). Likewise FCR
in aquaponics (0.97 – 1.39) (Endut et al., 2010; Pantanella et al.,
2011a) is similar to recirculating systems (0.94 – 1.29) (Degani et
al., 1988). In temperate areas some species may have interesting
market opportunities that specifically meet customers demand.
Aquaponics has proved to have good performances for sturgeon
grown at 19.5°C (FCR 1.01-1.25, SGR 1.38-1.66) (Dediu et al., 2012);
Murray cod (Maccullochella peelii peelii) reared at 22°C (FCR 0.8-
1.1; SGR 0.9-1.1) (Lennard and Leonard, 2006); and Largemouth
bass reared at 26°C (FCR 1.5; SGR 0.7) (Pantanella, unpublished
Figure 5.3 Okra and pak-choi produced by Svinna in
Figure 5.2 Lettuce (Lactuca
sativa) produced at Nibio in
Leafy vegetables fit well in aquaponics and most types grow well in aquaponic
systems. At Nibio in Norway the growing of lettuce (Lactuca sativa) (Figure 5.2) has
been successful in the pilot aquaponic systems. It has shown high growth speed and
it has been well received by customers. The price for good quality and single packed
heads is relatively high. Good varieties are green oak, crispy, green cos and butter-
head. Svinna in Iceland has grown the Asian plants pak-choi, malabar spinach and
okra (Figure 5.3) with good results in aquaponics with great consumer acceptance.
The main plant species grown so far in aquaponic systems is lettuce, which has been
grown under different densities (16 to 44 plants/m2) and crop lengths (21-28 days),
mainly on floating raft systems, and provided variable yields ranging 1.4-6.5 kg/m2 per
crop (Rakocy et al., 1997; Seawright et al., 1998; Lennard and Leonard, 2006; Dediu et
al., 2012). Basil is also a widely tested crop with densities of 8-36 plants/m2 that
brought to yields of 1.4 to 4.4 for crop cycles of 28 days (Rakocy et al., 2004a;
Pantanella et al., 2011b). Warm temperature crops also proved to be very productive,
as in the case of water spinach, yielding 33-37 kg/m2 in 28-days crop at a density of 100
plants/m2 (Endut et al., 2010), while okra could yield 2.5 – 2.8 kg/m2 in less than three
months at densities of 2.7 and 4, respectively (Rakocy et al., 2004b). Speciality and
culinary herbs such as salicornia and salsola could provide yields up to 7 kg in 110 days
and 5 kg in 28 days, respectively (Pantanella et al., 2011c; Pantanella and Rakocy,
2012). Thus, the annual plant production in aquaponics has shown to be varied
between species. In trials run by Savidov in Alberta Canada (Savidov, 2010), water
spinach and swiss chard made around 50-60 kg per square meter per year while
amaranth, lettuce, basil, choi, parsley and spinach made around 20-30 kg (Figure 5.4).
Figure 5.4 Annual production kg per square meter of leafy greens in aquaponics (Savidov, 2010)
Another interesting result from aquaponics testing is the difference concerning yield
between aquaponics and hydroponics. In mature systems aquaponics outperforms
hydroponics for tomato (31-59 kg/m2 vs 41-45 kg/m2) and cucumber (42-80 kg/m2 vs
50 kg/m2) with balanced N:K ratios (Savidov, 2005). Other fruity plants can still
perform well against hydroponics, such as the case of aubergine (7.7 kg/m2 vs 8.0
kg/m2 in 105 days) and tomato (23.7 kg/m2 vs 26.3 kg/m2, in 43-67 days), but cucumber
seems to show reduced performances (3.3 kg/m2 vs 5.2 kg/m2, in 42 days) (Graber and
Junge, 2009). Nevertheless optimal N:K ratios provide similar cucumber yields to
hydroponics (7.6 kg/m2 vs 7.5 kg/m2, in 48 days) and quality of fruits (sweetness,
vitamin C, dry matter) (Pantanella, unpublished data). For leaf vegetables there are
no differences between aquaponics and hydroponics for both lettuce and basil
productivity and leaf quality, both for chlorofill, leaf area, leaf to stem ratio and
nitrate content of vegetable tissues (Pantanella et al., 2011a, 2011b, 2012), also plant
growth in aquaponics nutrient water was higher. This study indicates that there is a
factor stimulating nutrient uptake and assimilation by plants grown in aquaponics
solutions, where nutrient and many organic compounds are derived from fish feed
(Savidov, 2010). Tomatoes, as well as most vegetables may also have assimilated
nitrogen in amino acid forms. Ghosh and Burris (1950) found that tomatoes use
alanine, glutamic acid, histidine and leucine as effectively as inorganic nitrogen
5.3 Quality and production of edible plants
So far plants growing in aquaponic systems tend not to get diseases. The plant
disease referred to as “pythium” or “root rot” (Figure 5.5), estimated to kill 30% of
hydroponically grown plants, is virtually unknown in aquaponics. The conclusion of
this is the fact that while hydroponic system is a largely sterile system, aquaponic
systems are full of beneficial bacteria and microbes that help plants to combat
disease (Bernstein, 2011). Nevertheless, integrated disease management must always
take into account the environmental susceptibility of the plant and the pathogen and
modulate the physico/chemical parameters to conditions that are more favourable to
the plants. Control of water temperature, ventilation, dew point, pH, optimal nutrient
balances are all abiotic parameters that help to prevent or control diseases. In the
case of phytium, the root rot disease, the pathogen spreads with favourable
temperatures above 27-28°C, thus control of water, together with inoculum of
beneficial organisms are a must, if the shift to alternative crops is not considered.
Nutrition for living organisms plays a fundamental role, as certain nutrients in excess
or in limiting concentrations favour the diffusion of pathogens. Nitrogen is important
for the vegetative growth of plants, but it makes plants tissues more succulent and
thus prone to attack of the pathogens if not correctly balanced with other nutrients.
During the production it is important to observe plant health and the colour of leaf.
Also the leaf shape can tell if the plant is doing well. Wilting and signs of stress can be
useful information for the producer to investigate plant health issues (root, collar,
vascular problems) as well as for nutrient unbalances.
If the crop is beginning to look unhealthy after the first few months it is a good idea
to check the nutrient profile of the water to find potential imbalances. These
imbalances can be caused by out-of-range pH. It is important to maintain pH between
6.0 and 7.0 for optimal nutrient uptake by the plants and good working conditions by
nitrifying bacteria. Also, it is imporant not to choose plants that prefer an acidic or
basic root environment, besides any other plant can be grown in this sustainable
system (Rakocy, 2011).
Plants need to have optimum growth rate to be a great partner in clearing waste
water from fish – and making aquaponics to a commercial economical winner. An
important issue is also the microbiological quality of aquaponics productions,
expecially for leaf vegetables. Besides the compliance to hygiene standards by
operators and plant management to prevent contamination by coliforms it may be
worth considering the use of sterilization to bring aquaponics within the water safety
standards for irrigation water. Past researches have already proven that aquaponics
are free from Escherichia coli, but a full control of coliforms withouth harming both
plants and fish should be possible (Pantanella et al. 2015).
Figure 5.5 Root rot from phytium (left) vs healthy roots (right)
5.4 Societal factors
It is important that cities reclaim foods that have characteristic of their community
strengthening the communal bonds between the residents. In addition, these foods
can generate jobs and revenue for the community (Yang, 2012).
Likewise, there has been a fast growing interest in urban farming in both developing
as well as developed countries since the world food crisis of 2007. The vulnerability
and dependency of food for the urban community already reaching 60% of the world
population, and its relience on a very concentrated food system made it clear for a
growing number city councils as well as a varied range of non-governmental
organizations (NGO‘s) that change in the foodsystem from ,farm to fork‘ had to
Aquaponics is becoming very popular among these various urban farm initiatives
around the world. This is especially true for community building in areas of
unemployment, food security issues and social problems; other factors include
educational awareness through giving a simple overview of the complexity of nature
Aquaponics related to urban farming are still based on small production units due to
first and foremost the requirement of a large plant area when more simple systems
are in use. The potential introduction of more modern biofilters or decoupled
production systems opens up for larger scale industrial based aquaponics. However,
the closer you move an urban farm away from the peri-urban zone to the inner city
center the more space becomes a physical issue as well as a constraint for
establishing a financially viable food business. The latter is true with regards to space
becoming a scarce resource in competition with other economic sectors. Therefore
the many “empty” or “free” roof spaces of a city has gained increased focus for
potential areas of food production, but requires often an expensive change in the
present building construction to carry an urban farm.
5.5 Risk analysis
A risk analysis (Table 5.2) shows the main risks in an integrated aquaponics
production system and how these can be minimized. The results show that
monitoring and controlling the crucial environmental parameters is essential to
maintain a healthy and stable system. The risk contingency plan includes the
prevention of pollution leading to fish and plant diseases, maintaining a secure
system control for a balanced environment, securing good quality of products and
understanding market needs.
Table 5.2. Risk analysis for aquaponics
Strict management procedures, dividing
production systems into units, controlling and
keeping a healthy environment and cleaning tanks
Strict management procedures, organic defences,
integrated pest management
Online monitoring and automatic control with
Oxygen level too
Monitoring and control, improvement of aeration,
reduction of stock
Failure of pH
Monitoring and control
Sodium levels too
Monitoring and control, shift to different feed
Failure of EC
Monitoring and control
Monitoring and control, safety procedures
Keeping good quality, fulfil official requirements,
and inform consumers about the production
Initiate emergency plan minimizing losses
6 Market and certifications
Aquaculture has quickly grown from a minor, niche industry into an industrialized and
modern one, and sustainability is at the center of many innovations on how to make
this arena a long-term and thriving success. Output for food production from
aquaculture has now surpassed that of wild capture fisheries, but also with having
growing negative environmental and social impacts.
In the past decade, internationally recognized standards regulating different facets
of the farming practice, from food safety to social accountability to environmental
sustainability, have gained a foothold in the aquaculture industry. The original
emergence of eco-certifications occurred as government agencies stepped away
from trying to regulate what constitutes sustainability. Although recently
governments have started to re-engage and increase participation in defining
ecological limits, certifications provide a voluntary regulatory interface, usually with a
No current certification scheme covers all of the issues essential to ensure that
products come from sustainable and fair aquaculture operations. Each certification
represents its own range of criteria and set targets. Some are species specific, while
others cover aquaculture production in general. Third-party standards dominate the
certification world, but there are also a few retailer-based standards or sourcing
It is then the responsibility of retailers to ensure that the products they buy come
from operations adhering to the conditions described above. Retailers must, until a
reliable certification system is in place, communicate to their customers the
sustainability of their products.
Product standards and eco-certifications act as shorthand for buyers at the
marketplace, a seal of approval to guide consumer decisions. Many producers are
learning that certifications are becoming a necessity to stay competitive at the sales
There are a number of incentives for producers to become certified. The certification
label provides an easy recognizable signal to consumers that a product meets a
certain level of performance, as defined by the standard. This can improve public
perception of farmed seafood in areas where consumers are more wary or where
there have been concerns regarding ecological impact. Although each certification
sets its own targets for sustainability, the process of certification provides
verification for producers since third party audits are required.
In addition to building legitimacy in the public eye, certification can provide
producers with access to certain retailers, and/or retailers and buyers that require
compliance with a minimum performance.
Market and certifications
6.1 Organic certification
Organic certification is of close interest to an aquaponics producer since the whole
system is based on a holistic thinking in terms of recycling, lowering the resource
intake and securing zero pollution. However, it is only possible to have a full
aquaponics production system certified organic if the plants are grown in soil, and
the fish produced are sold as fingerlings for further growth in open organic based
pond systems. There is a need for a review of these standards.
The regulatory framework for organic fish and horticultural production in the EU is
regulated by the Council Regulation (EC) No. 834/2007 whereas more detailed rules
are regulated by (EC) No. 889/2008, (EC) no. 710/2009 and (EC) 834/2007.
6.1.1 Horticultural produce
The present regulatory regime does not have any standards or regulations for
certifying organic aquaponics. The organic regulation only deals with separate
aquaculture and horticulture production. Each separate regulation hinders in various
degrees the prospects of taking a holistic approach and work towards an organic
certification for aquaponics.
For organic horticultural production current regulation 889/2008/EC, implementing
regulation 834/2007/EC, contains only one element specific to greenhouse
art. 4 which bans hydroponic production and allows organic cultivation only in soil.
Since most aquaponics production systems are based on a soilless hydroponic
technology, the plants produced under such a system cannot be certified as organic.
This opens the only option to adopt culturing practices on soil through decoupled
aquaponics/RAS waste water.
6.1.2 Aquacultural produce
For organic aquaculture the production is regulated by (EC) 889/2008 and (EC)
710/2009. In parr. 11. (EC) 710/2009 recirculating systems are clearly prohibited except
for the specific production in hatcheries and nurseries:
Recent technical development has led to increasing use of closed
recirculation systems for aquaculture production, such systems depend on
external input and high energy but permit reduction of waste discharges
and prevention of escapes. Due to the principle that organic production
should be as close as possible to nature the use of such systems should not
be allowed for organic production until further knowledge is available.
Exceptional use should be possible only for the specific production
situation of hatcheries and nurseries.
Since recirculating technology is the core of the aquaponics production system it is at
present not possible get an organic certification on aquaponics at all, and hence have
both fish and horticultural products certified as organic.
If the plants are grown in soil, like the IGFF system, it is possible to have the
horticultural produce certified as organic – but not the fish. As a contradiction to this
- within the organic regulation itself the horticultural produce is allowed to be fed by
a certain percentage of conventional fish feed, similarly to an organic plant
production receiving conventional manure.
The question remains whether it is possible to optimize the total finance in an
aquaponics production if the plant production is to be fed by a more expensive
organic fish feed, yet the fish are not allowed to be sold as organic and hence obtain
a higher premium.
6.1.3 Future of organic aquaponics
The crux for aquaponics producers to get an organic certification lies to get an
acceptance in the future of the recirculating technology.
Short-term strategies in this regard could be to:
1) View aquaponics as a farm based on a necessary harmony and biomass
ratio between husbandry (the fish), and a soil-based horticultural
production as the field turning waste into valuable resources and providing
a food production with no discharges to the environment.
2) Work towards a specific regulation on aquaponics. This would imply
allowing recirculating technology where a potential misuse of
intensification in the fish production is already guided by the organic
regulation on the number of fish allowed per m3 water, as well as a natural
constraint in the required horticultural production to use the fish nutrients.
Paragraph 24 in the (EC) regulation 710/2009 opens up for an interpretation that such
steps could be allowed:
Organic aquaculture is a relatively new field of organic production
compared to organic agriculture, where long experience exists at the farm
level. Given consumers’ growing interest in organic aquaculture products
further growth in the conversion of aquaculture units to organic
production is likely. This will soon lead to increased experience and
technical knowledge. Moreover, planned research is expected to result in
new knowledge in particular on containment systems, the need of non-
organic feed ingredients, or stocking densities for certain species. New
knowledge and technical development, which would lead to an
improvement in organic aquaculture, should be reflected in the
Market and certifications
production rules. Therefore provision should be made to review the
present legislation with a view to modifying it where appropriate.
Especially the last lines in Parr. 24 implies that national initiatives could be taken with
the aim of improving the common EU regulation on organic aquaculture. This would
require a more dedicated willingness in the organic movement to commence a
process in this direction.
7 Added value
Several added value products and services can be combined to the aquaponics
development to establish a viable business. Some of the implemented aquaponics
companies already have started aquaponics education based on their know-how,
skills and pilot units. The most famous aquaponics education is probably the
aquaponics training programme at the University of Virgin Islands
. However, many
other entrepreneurs have taken on the task to educate people in aquaponics.
Other ideas are byproducts such as using the sludge for crayfish production (Figure
7.1), worms (Figure 7.2), insects, or fertilizer production through aerobic or anaerobic
digestion. Also the aquaponic systems provide a tourism attraction in education
related experience. A visiting centre can be linked to the production unit, with direct
sale of products and even a restaurant as is the case in Tropenhaus in Switzerland
Eco-tourism is growing constantly over the last couple of years. Linking aquaponics
to tourism could be promising, especially as horticulture/hydroponics visitor centers
such as Fridheimar in Iceland (www.fridheimar.is) are booming. More central and
especially urban aquaponics installations combined with restaurant units and
education centers could raise awareness in that field and be an independent
economic business based on: tourism, education, food production, and gastronomy.
This is an excellent example of business diversification that could be a blueprint for
locations all over the world.
Figure 7.1 Red claw crayfish (Cherax
quadricarinatus) from Svinna´s pilot unit
Figure 7.2 Worm cultivation at Breen
Technology and equipment providers have been showing increased interest for
aquaponics in recent years. In general aquaponics have been moving from simple and
inexpensive boxes and home made units to industrial equipment used in
conventional aquaculture and horticulture as the systems become larger aiming for
commercial scale production. There is room for novel ideas that link the two different
production methods into one and this also includes monitoring and control systems.
8 Conclusion and future perspectives
The energy cost is increasing and the world is not only going through “peak oil” but
also “peak phosphorous”, making energy and fertilizer constraints on food
production (Ragnarsdottir et al., 2011; Sverdrup and Ragnarsdottir, 2011). Higher
energy prices directly affect food prices. At the same time the use of waste heat and
geothermal heat is suboptimized. Traditional aquaculture and horticulture produce
waste impacting the environment, waste that contains valuable nutrients that could
be circulated into other food products. Moreover, water scarcity is becoming a
problem in many countries due to climate change and changing precipitation
patterns. This is fast becoming a global problem and is inherently linked to resource
management, population growth and food security. Thus, the world needs new
technologies for optimum use of water, nutrients and direct use of waste heat and
geothermal energy for food production.
In aquaponics there is no waste, as all materials are valuable inputs in the production
cycle. Thus, aquaponics aims to mimic a natural system with optimal use of all
nutrients, water and energy. It uses no pesticides, herbicides, hormones or medicine.
Thus, it is an industrial chemical free production system. However, it may still be
difficult to have the production certified as the standards for aquaponics are under
development and traditionally organic certification of plants have required soil in the
system and RAS is not allowed in organic aquaculture.
At present, the interest in aquaponics is increasing globally. In Europe several strong
collaboration networks have been established e.g. the COST FA1305 Aquaponics hub
with 23 participating countries. Several ongoing projects in semi-commercial scale
aquaponics and research units are delivering results to support successfully-upscaled
aquaponic systems capable of contributing to a new integrated and sustainable food
Until now, aquaponic systems are coupled; which means RAS and hydroponics form
one loop or at least have common sump and filtration units. Decoupled aquaponics
would mean that those loops are separated enabling optimum environmental
conditions in both the RAS and hydroponics part eliminating trade-offs. Emphasis
would still be on zero-waste solutions and making maximum value out of all
resources. The first steps towards such systems have been taken and it will be
interesting to follow the future developments.
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