Aquaponics is the
integration of recirculating fish culture with hydroponic plant production.
In fish-only recirculating aquaculture, nutrient-rich water is removed
from the system and discharged to the environment on a regular basis
to manage nutrient levels within the system. In aquaponics, this nutrient-rich
water is seen as a commodity instead of a waste, and is used to grow
plants. Once the plants have utilized the nutrients and cleaned them
out of the water, the water is returned to the fish for further fish
culture, and the perpetual cycle begins again.
The advantages of
aquaponics are many, including:
miserly water use - the water is used very efficiently to grow two crops - fish & plants
zero environmental impact - no nutrient-rich waste-water discharge, the fish food is used to its maximum potential (to grow fish & plants)
two crops from the one input - the fish feed entering the system supports the growth of both fish and plants
small footprint/high density - because of their compact nature, facilities may be located very close to the end users (restaurants, green grocers, food manufacturers, public) in a variety of locations (country, city).
In addition, pesticides
and herbicides cannot be used to treat the plants, as these would
effect the fish, so the plant crops cannot contain any harmful chemical
An awareness of Aquaponic
technology is sweeping the world and there is a lot of information
available from various resources. However, it must be remembered that
Aquaponics needs to be adapted to local environmental conditions,
and especially, to local native fish species (and especially their
diets) , for it to be an efficient and viable technology.
An aquaponic system
consists of a number of components. These include: the fish rearing
component, the filtering component (both solids removal and biofiltration)
and the plant rearing component.
Most aquaponic systems around the
world rely on the use of the fish known as Tilapia. These fish are
not allowed in some countries, as they present a significant environmental
threat. Therefore, in these situations, we must rely upon native fish
species. Tilapia are a very hardy species, with much wider oxygen,
ammonia and dissolved solids tolerances than many other fish species,
and because of this, require far less filtering and water quality
control than many fish species.
The fish component of an aquaponic
system is very similar to a standard recirculating aquaculture system.
It comprises a fish rearing compartment (tanks), a solids removal
filtering component and a biological filtering component. The biofiltering
compartment is critical to aquaponic system design, because this contains
the most important biological entity of the system: Bacteria. Whilst
fish and plants provide the potential revenue or food sources grown
in aquaponics, the bacteria are the work horses of the system. They
allow harmful fish metabolite products to be converted to harmless
waste nutrients that may be used by the plants. It is this bacterial
conversion that is especially critical for aquaponic systems, as many
fish species are relatively sensitive to these metabolic toxins. A
good and efficient biofilter is an essential ingredient to successfully
run aquaponic systems containing many fish species.
There are a number
of different approaches that may be taken towards the design of an
aquaponic systems plant growth component. Probably the most often
used system is to adopt gravel beds for the hydroponic component.
This is a good method for small-scale, hobbyist or "backyard" systems,
as the gravel bed may act as the biofilter of the system. In addition,
if managed correctly, sometimes the gravel bed may also act as the
solids filter. However, caution is required here, for if solids build-up
and clog the gravel, it may lead to the establishment of "anaerobic"
zones (zones containing no or very little oxygen) which harbour bacteria
that can release toxins into the system. If solids are removed before
the water reaches the gravel bed, these systems can operate very effectively.
For larger scale
and commercial scale systems, hydroponic components are best designed
with no media in mind. Popular hydroponic components are deep flow
systems and NFT systems.
Deep flow systems
are generally large tanks of water where the plants are grown in floating
polystyrene boards that sit on the water surface. This allows the
plant roots to grow directly into the water. Many commercial aquaponic
systems use this method, as it is cheap to build, easy to manage and
maintain and requires no or little media for the plants. The plants
are placed into small, plastic net baskets that sit in wholes in the
polystyrene boards. This allows the roots to gain access to the water
and feed the plants the nutrients they require. This is the system
most commonly used.
NFT (Nutrient Film
Technique) is an hydroponic system consisting of many small "channels"
into which the plants are again placed using net baskets. A thin film
of water runs down the channel and allows the roots of the plants
access to the nutrient. The theory is that about 90% of the channel
area is actually air space, thus allowing the plant roots access to
plenty of oxygen.
Whatever system is
adopted, it cannot be denied that aquaponics is a fascinating food
growing system. To date, it is recognised as the most water efficient
food growing system in the world, and for a country like Australia,
that can only be a good thing!