Aquaponics — Where One Plus One Equals Three

In the beginning man was a hunter-gatherer, killing wild animals and harvesting wild plants for food. This nomadic life slowly changed when wild food resources declined and man became a farmer. Rumor has it that the wives became frustrated with continually moving the dishwasher from cave to cave!

Man is still primarily a hunter-gatherer in relation to food from the sea, but this can not continue indefinitely, as modern technology alone will ensure that the world’s fish resources decline at an increasing rate; fishing will becomes less and less efficient and attractive. The answer clearly lies in the hunter-gatherer of the sea being replaced by the farmer of the sea — aquaculture.

This is already occurring in a number of countries, such as Scotland, New Zealand, Norway, and Australia, where farming salmon in sea cages has become a major industry and where shellfish such as green mussels (New Zealand) and Rock Oysters (Australia) improve the efficiency of the industry.

In Australia there is also a significant freshwater fish farming industry producing eels, Barramundi, and Murray cod, but all of these land-based systems have two major problems — limited water supply and the disposal of fish feces.

I first became aware of aquaponics when I gave a seminar on aeroponics at the University of Western Australia. Two of the people who attended the symposium were from Curtin University — a postgraduate student from Cyprus and his supervisor. They took me to see the student’s research, which was growing a crop of NFT hydroponic lettuce together with the production of Barramundi fish. The system was quite simple in that in one large tank the barramundi were fed with fish food and the resulting solution was used as the nutrient solution for the hydroponic lettuce, which was then re-circulated back to the barramundi tank. Unfortunately, the student had to return to Cyprus and his PhD was never completed.

My next involvement with aquaponics was at the South Pacific Soilless Conference, which was held at Massey University in 2003. Among the papers was one from a Charlie Schultz from the University of the Virgin Islands in the West Indies. In his paper he described how he grew crops of basil in an aquaponic system with Tilapia fish.

In 2005 I attended a hydroponics meeting in Singapore, in which a whole day was set aside for discussions on aquaponics. Leading the discussion was Professor Jim Rakocy from the Virgin Islands, along with his colleague Charlie Schultz, whom I had first met at Massey some two years earlier. They were ably supported by a Canadian researcher, Nick Savidov, from Alberta.

In the Virgin Islands Shultz and Rakocy have developed over a 15-year period a very efficient technology for growing fish and plants in the same solution. They have found that the system requires a number of fish tanks in order to ensure a regular supply of nutrients for the hydroponic system. The problem is that the food supply to the tank containing the younger, smaller fish is much less than that for the more mature, larger fish, and therefore less waste nutrient is produced for the crop. If, however, the fish in the different tanks are a mixture of different ages, then the larger fish consume more feed, and produce more waste nutrient. Therefore, by having a number of different tanks containing fish of different ages a near constant supply of nutrients is available to the crop.

The hydroponic system used in the Virgin Islands uses the deep-flow method, and the solution is aerated regularly along the growing tanks. A similar system is used in Alberta, where the crops are grown under glass.

The fish waste has to have the solids removed before it reaches the hydroponic tanks, and this is easily achieved. The only possible problem with the system is that the fish prefer to live in a pH of about 7.0, and this can pose a few problems for hydroponic culture, because the trace element iron tends to become less available at high pH. This can be overcome by feeding the fish with an iron chelate, which provides iron to plants at high pH.

Worldwide there has been a steady move away from deep-flow hydroponic systems, but this system, with aeration undertaken throughout the deep channel by means of specialized aeration “stones,” means that the plant’s root system has access to a large quantity of water and a large buffer of nutrients. This could result in a considerable change in hydroponic crop strategy, because there is no doubt that the small buffering available when using NFT or rock wool means any loss of electric power can result in a total crop loss, unless there is a heavy investment in backup generators. This is unnecessary with a deep-flow system; the only loss would be in aeration, and the crop could stand a period without aeration. If considered necessary, a small standby generator could be incorporated into the system.

The nutrient solution is, in fact, very dilute, but because it is present in a large volume, the plant roots are able to extract all they need. Results in Canada suggest that after a few years yields can be even higher than conventionally grown hydroponic crops!

There is also the potential to sell the crop as a certified organic crop, because it is produced entirely from natural manure (fish waste). The system involves no control of root pathogens, as these are controlled biologically by the broad spectrum of antagonistic micro-organisms that develop in the natural environment.

In Australia, Wilson Lennard at RMIT University, Melbourne, has developed an aquaponic system to grow Murray cod in tandem with a recirculating hydroponic system growing basil. What kind of fish should we grow in aquaponics in New Zealand? With the recent development of a means to breed young eels in the laboratory (and an assured market for mature eels overseas), clearly this would be a good starting point, but another possibility might be to develop commercial trout farms. I appreciate the sport-fishing industry’s objection to this, but the risk of any trout diseases entering the wild when using a closed recirculating hydroponic system is minimal. If we wish to consider risk management, there are a number of trout anglers drowned every year — perhaps angling itself is too dangerous!

Of course, we have no information on whether we can, in fact, produce trout or eels in a recirculating hydroponic system, but I doubt whether we would be allowed to import either Barramundi or Tilapia fry into New Zealand from a quarantine viewpoint.

I have just returned from contributing to workshops on aquaponics in Brisbane, Sydney, and Melbourne, organized by journalist Geoff Wilson. Speakers included Jim Rakocy; Nick Savidov; Australia’s first PhD in aquaponics, Wilson Lennard; Geoff Wilson, and me.

The first workshop was held at the Bribie Island Aquaculture Centre just north of Brisbane. During the visit we took the opportunity to visit the Research Centre, which is salt water-based, and also the fresh water-based, commercial EcoFish International, near Caboolture, which produces both Barramundi and Murray cod. High fish-stocking rates are possible at Ecofish because pure oxygen (rather than air) is provided to the tanks. The main problem is the disposal of fish waste. The near-solid feces are relatively easy to remove, but the nutrient-rich solution cannot be recirculated back to the fish tanks until most of the ammonia has been converted to nitrate, and most of the nutrients removed. Currently this is being done with a large lagoon filled with aquatic plants, but with plans to triple fish production, an alternative strategy will be necessary. Aquaponics would appear to be an ideal solution. The hydroponics component of aquaponics will not only provide a second income stream, but will also remover a major source of environmental pollution.

Our next visit was to the NSW Fisheries Research Station at Port Stephens, just south of Coffs Harbour. A most impressive operation, but once again concentrating solely on salt-water aquaculture. We had also arranged to visit Taylor Made fish farms near Port Stephens, but at the last moment the invitation was withdrawn because the company had recently received heavy investment from the USA. It is understood, however, that Taylor Made does not use a recirculating system for their aquaponics, but the nutrient rich solution from the fish tanks is supplemented with additional fertilizer before being circulated through an NFT system growing lettuce, and then run to waste.

A brief visit the following day was made to the National Greenhouse Research Institute at Gosford, where we discussed with the staff the possibility of incorporating some aquaponics into their research programs. The day concluded with a meal in a restaurant in Sydney, where we chose the live Barramundi from the tank. Fresh fish is the key to the future!

Next day was the second workshop held at the most impressive Sydney Fish Markets and the following day found us driving towards Melbourne. Our next stop was the very impressive eel farm at Euroa, where eels are produced for fresh export to Asia. Apparently they ship with minimal losses by air freight, provided that they have a small quantity of water in a high-oxygen environment in a sealed polythene bag. Once again, this operation has a major problem with waste disposal, and an increasing environmental awareness by local government will ensure that improvements in waste disposal occur in the future.

The following day we visited the small-scale operation of Minnamurra Aquaponics, owned by Wilson Lennard and his business partner, Warren Watkins, and finally the Barramundi and Murray cod operation of Mainstream Aquaculture, situated in an industrial park near Weribee, in southwest Melbourne. At Mainstream the cost of waste disposal through the city treatment plant is a considerable burden on the company, and the potential for incorporating a hydroponics component to the system looks extremely attractive.

The only true aquaponics system we saw was at Minnamurra, and this was still in its very early days, but the potential for incorporating hydroponics into fresh water aquaculture would appear to be huge. Not only is there a further income stream from the operation, but also the problems of waste disposal are significantly reduced and, thus, the environmental impact from point source pollution is minimized. In fact, the real problem is not the solid waste (fish feces), which can be removed with relative ease and composted as manure, but the nutrient-rich solution, which is the environmental hazard.

In Canada, the Virgin Islands, and Australia, the income stream from the hydroponics has been greater than that from the fish. However, hydroponics income stream will depend very much on the choice of crop, and many of the “staple” greenhouse crops, such as tomatoes, cucumbers, peppers, and lettuce, will not produce the income that some of the more exotic crops are capable of producing. Basil, for example has been the most profitable crop in Canada, the Virgin Islands, and Australia, but there is clearly a limited market for basil or for any of the high-value herbs.

In addition, the staple hydroponic crops are not as suited to deep-flow hydroponic systems as many of the leafy vegetables. There is doubt whether they will grow well and, more to the point, the management may be more difficult with a deep-flow system, and converting a deep-flow aquaponics system to a recirculating coir-based system using drippers will require good filtration, along with some basic research.