Aquaponics for the Anthropocene

As the human population of our planet continues to escalate the fish farming industry is growing proportionately to provide nutrient dense fish protein for all these people to eat.  Fish farming in climates outside of the natural range of the species requires heating or cooling of the water, which in turn necessitates the utilisation of recirculating technology to justify the cost associated with temperature control.  Recirculating aquaculture systems (RASs) use powerful filters to trap and remove the solid wastes produced by the fish before these accumulate within the system and result in a reduction of the rate of fish growth.  Similarly, dissolved organic wastes are converted within the system from toxic ammonia to benign nitrate.  In this way a RAS enables the farmer to hold fish at high densities while only exchanging minimal ‘system water’ with ‘external water’, thereby making the temperature control cost effective.
 
In order for a RAS to keep working efficiently, the solids filter needs to be cleaned frequently, usually daily, resulting in water being lost from the system.  This water is full of organic `wastes’ largely comprised of nitrogen and phosphate which are each worth well in excess of R10 000 / ton, and every ton of fish feed converts to roughly 250kg dry mass of solids.  Dissolved organics within the system add to the total amount of fertiliser available; if only it could somehow be utilised …
 
There are ways in which the organic wastes from the fish can be utilised to fertigate crops.  The traditional method is to use this waste water to irrigate field crops, although this is wasteful in terms of the water budget.  An improved method is to grow plants in the same RAS as the fish, but in a different section.  In very simple terms the fish water goes into a mineralisation tank where the solid and dissolved wastes are converted into dissolved fertiliser including both macro and micronutrients.  Next this water travels to the plants which take up the nutrients to grow and fruit (depending on the crop being grown), thereby stripping the organics from the water which is then ‘clean’ to return to the fish.  This technology is known as Aquaponics from the root words AQUAculture and hydroPONICS, as it is essentially hydroponics and aquaculture in synergy with each other.
 
See below the stylised layout of the components of an aquaponics system showing the water flow direction.
 
Aquaponics offers many advantages over just hydroponics or just aquaculture.  The obvious first point detailed above is that the fish waste is utilised to produce a second crop at very little extra cost.  However, the greatest differentiators are the healthiness and flavour of aquaponics crops.  Due to the very natural processes behind aquaponics we find that disease and pest pressure are low, such that a disciplined program based on green label pesticides is adequate to control plant pests.  This is important not only for the consumer who eats the crops, but also for the fish and desirable bacteria living in the system; they could be negatively impacted if any plant pests were sprayed with heavy chemicals.  As for the flavour, there is simply no comparison between the taste of aquaponically produced crops versus other farming methods.  The cucumbers are delicious, the rocket and tomato are bursting with flavour and even fairly bland crops like lettuce become juicy, crunchy and tasty.
 
Other advantages of aquaponics include the very low water usage and that the system can be placed where there is no arable land, making it highly suitable for installation in desert situations. 
 
Schools can teach many valuable lessons in aquaponics systems; aquaponics systems can be installed in refugee camps and prisons to provide food for the residents and offer a training opportunity to up-skill the refugees and inmates. 
 
The options are almost endless, but most importantly aquaponics is a technology that produces nutritious, delicious crops for the populace in a manner that is light on the planet.
 
For further information on aquaponics send us an email on leslie@aquaculturesolutions.org.