I have been a hobby grower using aquaponics for several years. I have had reasonable success although also some difficulties. I am considering setting up a commercial operation and have been reading your answers and articles on planning for commercial hydroponic growing. Would you have any extra advice relating to aquaponics, possibly organic?
Answer by RICK DONNAN
I’ll answer this in general terms so it is useful to a wider range of readers. In simplest terms, aquaponics is the integration of aquaculture (to grow fish) with hydroponics (to grow plants, usually vegetables).
There is a significant and increasing proportion of edible fish grown in aquaculture around the world, especially in China. Often aquaculture is thought of as sustainable method of getting fish, rather than depleting sea fish stocks. The reality is quite the opposite. What is the major food for fish being grown in aquaculture? It’s lower value fish and it takes about two kilograms of this fish food to produce a saleable kilogram of higher value aquaculturally grown fish, and higher still for carnivorous fish. This is obviously not sustainable.
With the certain continued expansion of aquaculture there is an urgency in finding alternative non-wild fish sources of food for aquaculture. One of the most promising possibilities is to grow saw fly larvae. The flies lay eggs in vegetable waste and the eggs hatch to become larvae (maggots). These maggots grow quickly feeding on vegetable waste then can be separated and processed into high fat and protein content fish food. There has been a lot of research done on these larvae, resulting in the development of commercial scale production facilities, which are expected to come on stream soon.
Aquaculture technology and difficulties
A basic part of pond and tank aquaculture is to continuously recirculate the fish water. Once they have eaten, the fish pass solids and urine. The solids can be filtered out, but the urine contains ammonium ion, which can build up through the recycling of the water. If the ammonium gets high it is toxic to the fish, so it must be removed. This is done by passing the water through a bio-filter, also called a bio-reactor. The biologically active population first converts the ammonium ion to nitrite ion, then to nitrate ion. While much less toxic to the fish than ammonium, the nitrate must not be allowed to rise too high, hence it must be bled off. The result is a high nitrogen content waste stream, the disposal of which is a major problem for aquaculture.
Why not turn this waste stream into a useful feed for something that will use it? Like a hydroponic system!
This could be done by feeding food to the fish that results in their waste stream being of a suitable nutrient balance for use by the plants. Unfortunately, it is not quite that simple.
The optimum solution properties for the fish and for vegetable plants are different. For example, for barramundi compared to leafy greens:
• pH: 7.4 compared to 6.2
• Water temperature: 28o – 30oC compared to 20o – 25oC
• Nutrient level (EC): low compared to higher
• Salt level (sodium chloride): high compared to low
• Chemical sprays: never, compared to sometimes
• The nutrient balances needed are different, especially for fruiting plants.
These differences need not be critical, but require significant compromise to be combined to become an aquaponics system.
A basic system consists of at least one fish tank then a bio-filter and a hydroponic system. The hydroponic system is typically media-based beds, often using expanded clay, however, it can also be a water-based tank or channel system. Tying the system together in order to recirculate are pumps and pipes. Hobbyists can build their own system or buy a prefabricated system.
There are websites, blogs, magazines and books to help the beginner. It tends to be heavily promoted as easy and there are many successful hobby growers, however, failures and death of fish or plants, or more often both, are common.
In commercial aquaponic production, the different requirements, especially nutrient balance, in the fish water compared to the hydroponic water are a major difficulty. Consequently, most modern commercial aquaponic operations in Australia use the fish waste stream as an input into the hydroponic system. That is, although the hydroponic nutrient solution is recirculated, this is done internally, and it is not returned to the fish tanks. This enables the solutions in the fish tanks and the hydroponic system to be independently optimised.
While the step from being a hobby grower and moving to commercial production often seems a minor change, in reality it is actually huge.
It is fun to grow your own veggies, harvest them when just ripe, and they seem perfect because you grew them. Commercial production is different. You have to produce a consistent product to specification, harvested to schedule and allowing for delays in the food chain. To do this probably requires investment in a greenhouse and sophisticated aquaponic system. You must know your crop extremely well, how to cultivate it, control pests and diseases, optimise its environment and nutrition, etc. For aquaponics, you have the extra requirement for expert knowledge of how to manage your fish. As for any small business there are the range of management aspects that you have to be on top of.
Marketing becomes crucial. Once growing successfully you must be able to sell your produce for a price that makes it all worthwhile.
A failure as a hobby grower is not a problem – you just clean out and start again. As a commercial operation, losing a crop (plants and/or fish) might be a fatal financial disaster, especially if you also lose your market because it required consistent supply.
Using an aquaponics system to remove a waste aquaculture stream from the environment is a good move for sustainability and therefore is often thought of as organic. However, this is usually not the case. I am referring here to organic certification, which is the aim of most commercial aquaponics growers.
The difficulty comes with the hydroponic part of the system. There are organisations, which give organic accreditation, and what is critical is that organisation’s (or the government’s) definition of ‘organic’. Many define organic as having to be grown in the soil. For these organisations hydroponic and aquaponic systems can never be organic. (For example, in the US, some states require growing in the soil and others do not.) Those other organisations, which don’t limit ‘organic’ to soil growing, have other differing requirements as to what inputs are allowable. Meeting all these requirements is usually very difficult. RD
PH&G July 2017 / Issue 181