Feature Article: March, 2010
In the beginning man was a hunter-gather.
This nomadic life slowly changed when food resources declined and men became farmers.
Man is still primarily a hunter-gatherer in relation to food from the sea; however, the world’s fish resources are declining at an increasing rate, making fishing a less efficient and less attractive option. Only about four per cent of the world's oceans remain undamaged by human activity, with climate change and fishing being the strongest influences.
The answer clearly lies in the hunter gatherer in the seas being replaced by the farmer of the sea with aquaculture. This is already occurring in a number of countries including Canada, Scotland, Chile, New Zealand, Norway and Australia.
In Australia there is also a significant fresh water fish farming industry producing eels, barramundi and Murray cod, but all of these land based systems have two major problems, namely the limited fresh water supply and (even more critical) the disposal of the nutrient rich waste products from the fish.
So what is aquaponics?
I was first introduced to aquaponics when visiting Western Australia and met with two people from Curtin University; a postgraduate student from Cyprus and his supervisor. The student’s research involved the production of fish (Barramundi) combined with growing a crop of NFT hydroponic lettuce.
My next involvement with aquaponics was at the South Pacific Soilless Culture Conference held at Massey University. Among the papers was one presented by Schultz from the University of the US Virgin Islands in the West Indies. In this paper he described how he grew crops of basil in an aquaponic system with Tilapia fish.
At a hydroponics meeting in Singapore, a whole day was set aside for a discussion on aquaponics. Leading the discussion was Professor Jim Rakocy from the US Virgin Islands, along with his colleague Charlie Schultz. They were ably supported by a Canadian aquaponics researcher, Nick Savidov from Alberta in Canada.
An aquaponic greenhouse showing plants being supplied nutrients from their fishy counterparts (above left). Tilapia, a common species, thrive in their own tank, providing nutrient-rich water to the plants.
A visit was made to the aquaponics project of Dr. Jim Rakocy and Charlie Shultz at the University of the Virgin Islands in the West Indies. Water is a very scarce resource on the Island of St. Croix and all the water for the project is collected as rainfall on a large plastic sheet, and stored in a deep reservoir. Essentially, the only water being lost from the system is through transpiration, as all the other water is re-circulated from the fish to the hydroponics system, and then back to the fish.
The US Virgin Islands is considered tropical, and so all the crops are produced without any protection. Rakocy and Shultz have found that they require at least four different fish tanks to ensure a regular supply of nutrients for the hydroponic system. It is not possible to mix fish of widely different ages (sizes) in the same tank because of the risk of cannibalism. They have also found that it is desirable to grow plants of different ages, to ensure that the uptake of minerals by the plants is also evened out over time.
The fish waste has to have the solids removed and much of the ammonia excreted by the fish converted to nitrate before it reaches the hydroponic tanks through the use of a bio-filter. Simplistically, a bio-filter may comprise only a section of windbreak mesh, through which the solution slowly passes. Over a short period of time, a broad spectrum of micro-organisms becomes established around the bio-filter. Some of these micro-organisms are capable of converting ammonia to nitrite, and others can carry out the next step of converting nitrite to nitrate.
The hydroponic system used in the Virgin Islands is the deep flow method (DFT), and the solution is aerated regularly along the growing tanks.
I visited the aquaponics project of Dr. Nick Savidov at the Horticultural Research Institute in Brooks, Alberta, Canada. With winter temperatures below -22°F, this environment could certainly not be considered tropical.
From a horticultural viewpoint, Savidov has shown that not only does a recirculating aquaponic system results in fewer root diseases in the crop, but also that the crop yield from aquaponics, when compared with conventional hydroponic, is often increased.
The reduction in root disease is not surprising, as there is considerable interest in Europe in developing an ecological balance of organisms in the nutrient solution, as clearly a sterile solution is not sustainable even in the short term. The deep sand filters being developed in Europe for recirculating hydroponics systems are a good example of this approach.
There is no simple explanation for the increased yield reported by Savidov, but one possibility is that the organic components in the nutrient solution (possibly humates) may make the trace elements more readily available to the plants. A recent report of microbiologists with the Alberta Research Council (ARC) has shown a presence of so called Plant Growth Promoting Rhizobacteria, or PGPR, in aquaponics water. There is no doubt that the UV sterilization of the recirculating nutrient solution undertaken in conventional hydroponic systems has the potential to alter the microflora population and composition plus precipitate out iron; these factors alone may be enough justification for moving away from the conventional hydroponic systems.
“Aquaponics is not just more efficient and environmentally friendly than other technologies, but it is also a safer way to produce vegetables.”
The key factor in aquaponics is that the plants are grown using a deep flow hydroponics system. However, worldwide there has been a steady move away from deep flow hydroponic systems towards Nutrient Film Technique (NFT) and media based systems that use, for example, rockwool or coco peat (coir). Using a deep flow system with forced aeration throughout the deep channel by aquarium aeration stones, means that the plant root system has access to a large quantity of water, and also to a large buffer of nutrients without running short of oxygen. In aquaponics the nutrient solution is actually more dilute than in conventional hydroponics, but because it is present in a large volume, the plant roots are able to extract all they need. In tests strawberry plants were grown in NFT and coir using aquaponics water from a DFT facility as a source of nutrients. The leachate was then returned to the DFT facility. The trial showed a potential for aquaponics operations to successfully grow greenhouse crops using several techniques while providing an opportunity for diversifying aquaponics operations.
A new aquaponics facility was constructed at CDCS in Brooks using expertise acquired from working with the previous model. In the new facility the research team managed to:
- Radically improve usage of greenhouse space by more than two times. With the same gas bill the producers will be able to double the yield of greenhouse crops.
- Significantly decrease labor requirements through new design and better protocol for crop management based on the design.
- Entirely eliminate water discharge from the system. It is a completely contained system now, which allows introduction of new fish species, for example, barramundi in North America, without any contact with the environment. No fertilizers or pesticides were used to produce greenhouse crops. The developed system is unique by its efficiency in space, labor and water usages, and its environmental impact is close to zero. The new design allows aquaponics operations in a fully automated regime and shows a high potential for considerably larger operations incorporating integrated waste management.
A study/survey on bacterial contamination and a spoilage rate of green vegetables was conducted at CDCS. The leaves were collected in aquaponics and compared to the green vegetables purchased in grocery stores. The aquaponics produce showed minimal spoilage compared to other samples. This confirmed previous two-year food safety studies, which showed no presence of E. Coli or other pathogens in aquaponics produce. It is not a surprising result as the plants are grown in a confined area with no contact with animal manure, which is a main source of E. Coli contamination in field-grown produce. Thus, aquaponics is not just more efficient and environmentally friendly than other technologies, but it is also a safer way to produce vegetables.
Omega 3 (ω3)
One interesting aspect of aquaponics is that one of the critical human health constituents found in fish are the Ω3 fatty acids. There are essentially three Ω3 fatty acids, namely DHA (important for brain health), EPA (important for cardiovascular health) and ALA. DHA and EPA are only found in seafood, and are derived by fish from the consumption of micro-organisms consumed at sea by fish etc. EPA is found in a range of plant derived seed oils, e.g. hemp seed oil, but our bodies are only able to convert small quantities (10 per cent) of EPA to the physiologically active DHA and EPA. Thus to ensure an adequate level of EPA and DHA in our diet it is necessary to consume fish which contain these fatty acids. This does not mean that the fish must be sea fish, but that the fish must have been provided with a source of DHA and EPA, which means that they must have been fed with fish meal sourced from sea fish.
Education and Agritourism
As society becomes more urbanized, a separation is developing between those with a rural background and those who believe that food comes from the supermarket. Aquaponics provides a very suitable educational vehicle to demonstrate the link between animals (fish), fish waste, plant nutrition and human food. It also provides an excellent example of the need to have a balanced ecology.
Agritourism provides a valuable interphase between urban and rural, and between the developed and developing world. Jon Nielson, a teacher from Rosemary High School (Alberta), successfully introduced aquaponics as part of his biology and chemistry curricula using aquaponics mini-systems developed at CDCS. As a result, the average marks in biology increased by 20 per cent and has prompted other schools in the district to consider aquaponics as a teaching tool for biology and chemistry teachers.
Conclusion
Aquaponics is an ecologically sustainable system capable of producing food with few, if any, pesticide residues. Preliminary studies have demonstrated it is worthy of further investigation and development as a commercially viable business.
There is one added marketing advantage of aquaponics and that is that provided the pesticides used to control pests and diseases conform to organic criteria, then clearly the crop could be organically certified.
Other articles by Mike Nichols
