Aquaponics is simply a combination of aquaculture and hydroponics. In a nutshell, fish waste that has been generated by fish food is pumped from the fish tank to neighbouring grow beds. Plants grow exceptionally well on this continuous supply of nutrient-rich water. The ‘cleansed’ water can then be returned to the fish tank. For a more complete explanation follow this link about what is aquaponics.
But why should anyone consider aquaponics in preference to either a pure aquaculture or hydroponic system? This article will consider the major features of this method of food production. Over the last couple of decades aquaponics has grown enormously in popularity, especially in countries such as the USA and Australia. A proper understanding aquaponics uses, and its limitations, is a key requirement for success.
Aquaculture has also expanded rapidly over this time to become an increasingly important source of fish. As a result of our greed, and poor management, our fisheries have sadly declined. Recirculating aquaculture systems (RAS) represents an exciting and developing sector of aquaculture. RAS utilise a range of water treatment processes to enable the effluent from the fish rearing tanks to be purified and returned. This not only greatly reduces the water requirements (up to 90% less water) but allows much greater control of the fishes environment.
What are the Benefits?
The aquaponics benefits are many and varied. Every system is different and usually reflect the hopes and aspirations of the operators. What one operator considers essential another may dismiss as unimportant. A koi keeper may wish to favour water clarity over growth rate whereas a home food producer would prefer to produce a bumper harvest of a range of plants. Notwithstanding the above the following are generally recognised as some of the more important benefits.
i) 90% Reduction in Water Requirements
A distinguishing feature of aquaponics is that the water, and nutrients, are retained within channels that prevent water loss through natural drainage and soakaway. As a result there is typically a massive 90% reduction in water requirements. This opens up production capability in many new areas that have low natural water reserves. This is the main reason for it’s popularity in areas such as Australia and Texas in the USA. It also allows use to use the limited municipal water supplies available in urban areas.
ii) Faster Growth Rates and Higher Productivity
Several features of aquaponics combine to help promote faster growth rates both of the fish and the plants. The fish;
- gain from better water quality. In particular, higher dissolved oxygen levels and lower ammonia levels
- The reduction in water requirements brought about by the recirculating system (RAS) opens up the potential to control the fish tank temperature . This has a profound affect on fish growth and feed conversion.
The plants show significant increases in growth rates over conventional soil culture because;
- Water is never in short supply in spite of overall lower usage rates.
- Fish are continuously and consistently producing plant nutrients.
- Plant roots are continuously and consistently being fed nutrients by the pumps.
- The continuous supply of water also brings a continuous supply of oxygen directly to the roots.
iii) Indoor Culture Feasible
A lack of dependence on suitable soil conditions, water supply and great control of a higher productivity has opened up the potential to site aquaponic systems inside buildings. The advantages of greenhouses and polytunnels is well recognised in traditional horticulture and applies equally to aquaponic systems. The development of modern lighting systems has allowed the siting of aquaponic systems within a wide range of otherwise redundant buildings and basements. Urban community farms have embraced the opportunities presented by aquaponics. Year round production is now a reality.
Other important benefits of aquaponics brought about by indoor culture include;
- the ability to site farms close to local markets.
- it is easier to cater for niche, local markets.
- Greater protection from predators such as herons and fish-eating mammals
- Elimination of soil borne plant diseases
- Elimination of certain fish diseases that rely on other pond inhabitants for transmission. I have escaped the potential dangers of the blood fluke, Sanguinicola sp. because of the lack of water snails in a RAS carp system.
- With increased environmental control it is usually possible to artificially spawn fish throughout the year. This is an important when higher productivity is essential to cover increased pumping and heating costs.
…. and the Cons
Having read all the wonderful news about aquaponics you would wonder why this technique has not enjoyed greater success. Indeed, over the last few years there have been many aquaponic failures involving significant investments. This may be expected in a developing industry but it is important to try to identify common causes.
i) Higher energy requirements
Pumping, lighting and heating costs can be significantly greater than traditional culture methods. In China, pond culture of tilapia is very low cost, making it difficult for western aquaponic system to compete. Heating costs of greenhouses in much reduced in Mediterranean areas compared to more temperate zones such as the UK.
ii) pH requirements compromised
An aquaponic system is composed of three living components. Namely the fish, the plants and the biofilter bacteria. Generally speaking the fish are highly adaptable and a pH 6 – 8 is normally fine. On the other hand plants prefer a pH around 6 – 7 whereas the filter bacteria grow best at pH 7 – 8. This is not a vast difference but it can be significant. At pH’s best suited to nitrification plant nutrients tend to become less available. To a large degree this deficiency can be overcome with careful supplementation, particularly of iron. Careful selection of suitable plant species is important. For instance , it has been suggested that cucumbers grow better at higher pH than say tomatoes.
iii) High Dependance on Power Supply to Maintain Life
A suitable automatic fail-safe power system is a prerequisite of most commercial aquaponic systems. Catastrophic fish mortality can occur in minutes if the stocking density is high, through the depletion of oxygen. Most of the RBC systems that I have operated needed such a system. Failure inevitably lead to 100% mortality of the fish with about 20 minutes. Plants in NFT systems are also vulnerable to drying out if the water fails to flow. As such they are not so well suited to small-scale aquaponics systems.
iii) Lack of Skilled Operators
Production system design and management need to balance the needs of three living and interdependent organisms, namely the fish, the plants and the aquaponic bacteria. Excessive production regimes can quickly upset this balance and overcome the natural desire to maintain a balance. Generally speaking everything works well, but occasionally, and almost inevitably, something will go wrong and need immediate correction. Skilled and experienced staff are essential in getting to know how a system is performing.
Not only are novel species of plants and fish constantly being assessed from a production capacity there is always the need t develop new and novel markets. Higher production costs need to be off set by customer acceptance that food grown in an aquaponic system is superior to traditional growing methods. Lack of pesticides and artificial fertilisers need to be fully appreciated by the customers.
Reaping the Benefits of Aquaponics
The inherent variability of aquaponics poises many challenges, especially if profitability is a prime driver. Local niche markets do command better prices but production levels must be appropriate. Too small and the extra energy costs can prove prohibitive. Too large and the wholesale prices fail to meet requirements. Aquaponics excels at producing fresh local plants and live local fish. One universal piece of advice is start of small and expand and improve technology as the market develops.