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Aquaponics: The Low-Down

tomato

Clockwise from top: An abundance of tomatoes in summer; The floating raft beds in front of the scoria beds; Fat trout harvested from the tank. Photos by Ben Pohlner

aquaponics
aquaponics

Aquaponics combines aquaculture and hydroponics to produce fish and plants in one integrated system, creating a symbiotic and mostly self-sustaining relationship.

Combining fish and plants isn’t a new concept, with its origins dating back several millennia. Asia’s rice paddy farming systems is an example. Aquaponics today borrows and combines methods primarily developed by the hydroponics aquaculture industries, along with new ideas from the innovative DIY online community.

HOW IT WORKS

The basic principle of synergy involved in aquaponics is the requirement of clean water to promote the healthy and fast growth of fish, and the need and ability of plants to use nutrients from the water to grow. One of the most critical aspects in this relationship between plants and fish is the diverse microbial community which transforms fish wastes into forms of nutrients more easily used by plants for growth.

In the simplest arrangement, you will need a tank for fish and a trough for plants. Given that plants require physical support for their roots to extend into, some kind of growing substrate is required in the trough. Often quarried gravel, scoria or manufactured clay pebbles are used. More advanced growers tend to use a raft system. A raft usually floats on the water, allowing the plant roots to hang into the water.

The substrate is often the most important design feature as it is vital in supporting and promoting the microbial health of the system. Microbes coat the gravel, so as the water is recirculated between the fish tank and the planted trough, the fish wastes are filtered which produces clean water for the fish.

WHY AQUAPONICS?

Aquaponics systems use about 90 per cent less water than soil based food production, which is why aquaponics systems are often established in deserts and islands (where freshwater resources are precious). In many of these locations, fresh fish, meat and vegetables are also at a premium due to high food miles, making local aquaponic produce a more sustainable option. Aquaponics can also provide access and food sovereignty to people in locations where soil fertility may be low or where risk of soil contamination exists.

The full life cycle analysis debate is well underway, the answers to which are situational and not easily arrived at given the complexity of the global food system.

Plant growth in aquaponics is very quick, with high productivity from a small area. This is the same for fish growth, with people easily growing 10 kgs of fish for each cubic metre of water in a simple backyard system.

For the backyard enthusiast or school environment, aquaponics as an educational tool can cover the most basic concepts of biology and ecological systems to the more complex interactions of water and microbial biochemistry. These systems can also be designed to mimic local aquatic ecosystems and make for fantastic observation. On a practical level you can explore construction, plumbing and the tricky balance of growing fish and vegetables simultaneously. It is very much a multi-skilled project!

MAINTENANCE

Like all gardening, there is always regular maintenance, and aquaponics is no exception. However there is a certain labour of love that goes along with aquaponic growing, especially for the beginner.

The day-to-day maintenance requires fish to be fed once or twice a day, keeping an eye on fish behavior and health to avert disease. The system’s water level and pump need to be checked, making sure the aerator is running and supplying oxygen to the fish. Every few days it’s time to check your water quality and adjust where needed; a crucial task. This involves a range of reasonably simple tests you can buy from an aquarium shop.

Once you get the hang of it, tasks will speed up, requiring less effort. Aquaponics for the most part requires far more attention to detail and time while you’re learning.

aquaponics
An abundance of vegies. Photos by Ben Pohlner
aquaponics
Smoked trout. Photos by Ben Pohlner

NUTRIENT VALUE OF PRODUCE

There has been a long-running debate on how the nutritional quality of vegetables produced in aquaponics compare to that of conventional or organic produce. Aquaponic systems derive their nutrition primarily from the water in which they are grown. These nutrients are largely derived from the breakdown or mineralisation of fish wastes and ultimately what nutrients are contained in the feed. The trouble here is that not all of the nutrients required by plants are contained in the fish feed.

Most people will add chelated iron along with potassium and calcium as buffers to keep a constant pH. The pH of the water is a crucial aspect to both plant and fish health. Once the water starts to approach a pH of 7, these nutrients will become unavailable to plants, impacting how healthy and nutritious the vegetables become. This is where the aquaponic gardener is kept on their toes. Unlike the slower changes in a home garden in the soil, aquaponics systems are much more dynamic and in need of attention.

HOW TO INCREASE NUTRIENTS IN PRODUCE ORGANICALLY

There is a growing body of literature and experience pointing to a way in which aquaponics and hydroponics can remove or greatly minimise the need for artificial nutrients to be used. It is reasonably common practice in agriculture for farmers to use compost, worm castings and worm teas to increase soil fertility. This is the same in aquaponics, with many backyard growers adding straight worm leachate, worm tea and compost teas to their systems. What this relies on however is that wastes with the right micronutrients are added to the worm farm. And for buffering the pH, some people use oyster shells.

With any intensive system like aquaponics, at some stage you will likely have to add an amendment. One amendment that many growers use periodically is seaweed extract. This can be added to the water or used as a foliar spray. Creating diversity in the nutrient and mineral base, as well as promoting a strong microbial community, will put the grower on the path of healthy and nutritious plants.

IS AQUAPONICS VIABLE?

Aquaponics offers a lot of advantages, primarily in its ability to produce vegetables and fish with a very low overall water demand. In locations where vegetable produce has high food miles and is not produced locally, aquaponics can have a comparatively small environmental footprint. Although often it’s likely that aquaponics has a bigger environmental footprint than other types of vegetable production.

If there is sustainable local fishery, good rainfall, and fertile soil, it is likely that supporting or engaging in regular home gardening in the soil and buying fish locally (or going fishing yourself) might be more sustainable. In most cases, aquaponics uses a reasonable amount of energy to continuously recirculate water and to provide oxygen through aeration for the fish and plants. The home grower will also need access to good quality fingerlings and fish feed to keep their systems going.

IS IT A SUSTAINABLE OPTION FOR LARGESCALE GROWING?

Due to climate change, rainfall in many regions is diminishing and becoming increasingly variable, with more hot and extreme weather. Across a range of food production systems there has been a steady transformation with the harnessing of new technologies to optimise growing conditions. Aquaponics at the commercial scale is a highly technical operation which offers a great degree of control.

So as we face the uncertainties of climate change, aquaponics can certainly offer an alternative way to grow both fresh vegetables and fish. Although it should be noted that aquaponics is mainly suited to salad greens such as lettuces and herbs, fruiting vegetables and micro greens. However it will not give any security to the global staples like maize, rice, wheat and potatoes.

BACKYARD SETUP

Ben Pohlner, Warrnambool, VIC

aquaponics
Photo by Ben Pohlner

Ben’s backyard system consists of a 7.5 m x 1.6 m x 0.8 m tank with two scoria filled grow beds sitting on top, a range of floating raft beds and storm water pipes running up the sides with lettuces growing out of them. At the end sits a worm farm that drips worm leachate into the tank. Herbs, tomatoes, onions, celery, lettuces and strawberries are grown on top with barramundi grown in the tank.The water from the tank not only circulates within the system but is also pumped out onto vegie garden.

Operational cost/year:

100 fingerlings at $1.28 each = $128

4 bags of feed @ $92/bag = $368

Electricity 35w x 24hrs x 20c/kw av (peak/off peak) = $62.05

Total running cost/year $558.05

Kilo of fish produced = 78.8kg

$7.08/ kilogram

Plus more than enough vegetables to feed a family of four!

COMMERCIAL SETUP

Green Camel, Sydney NSW

aquaponics
Photo by Ben Pohlner

Green Camel is a certified organic integrated fish and crop production system operating on a commercial scale. It is located in Western Sydney on land owned by the University of Sydney. The system operates as a semi-closed biosphere (inside a glasshouse), allowing the crops to grow all year round. Waste from fish production is captured and transformed into plant available nutrition allowing maximised plant production. It operates using a Moving Gulley System (MGS) for leafy green produce production, suspended above a Recirculating Aquaculture System (RAS) producing barramundi.

They grow commercial quantities of fresh basil, coriander and parsley, sold through a major supermarket chain and the fish are sold to restaurants. The system operates without the use of synthetic pesticides, fungicides or inorganic fertiliser inputs.

All crops are certified organic.

Size: 4320 sqm

Output:

  • 130,000 kg of high quality organic herbs
  • 15,000 kg of barramundi per year

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