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Intensive Tilapia in a re-circulation
'green-water' system |
How much water is actually needed for large-scale
fish farming?
This is a cardinal question, as it influences water source and site
selection, investment, operating costs and the environmental sustainability
of the project. Water is needed to provide a ’home’ for the fish. Water flow
and water exchange are needed in order to remove wastes and ammonia produced
by the fish, and to supply oxygen.
Clean and abundant water sources are not readily available, and must be
protected environmentally.
It is therefore essential to reduce dependency on external water supply.
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How can I reduce water requirement, yet maintain large-scale production?
Using APT ‘green-water’ re-circulation system, Tilapia fish
farms enjoy the following advantages:
 Significant
reduction in daily water requirement for ammonia and waste
removal.
Possibility
to pump only several hours per day (not during low tide, or mud erosion).
Reduced capital investment (pumps, pumping installations, electrical
system).
Reduced operating costs (lower electrical consumption for pumping).
Increased environmental sustainability – all wastes are treated within the
project area.
More flexibility in site selection (the selection of the water source is
less stringent).
Can I see APT’s ‘green-water’ re-circulation system at work?
View APT’s large-scale Tilapia projects in
Belize (1,300 ton per
year) and
El Salvador (1,600 ton per year).
Semi-closed water system design, based on re-circulation of green-water between production ponds and reservoirs.
Wastes in the water (ammonia, fish
feces and uneaten food) are treated within project boundaries, facilitated by
the high oxygen level maintained in the 'green-water' system.
How does it work?
The waste produced by the fish is comprised of highly digestible particulate
matter, dissolved nitrogenous compounds and minute additions of phosphorus
derived from fish excrements and decomposed feed. Treatment is accomplished
by the action of the natural populations of bacteria and algae, which thrive
in the reservoirs and earthen ponds (hence - 'green water'). These carry out heterotrophic
decomposition of the organic waste, followed by oxidation of the ammonia
to nitrite and nitrate through nitrification and de-nitrification, by the
certain bacteria (Nitrosomonas sp. and Nitrobacter sp.).
The
nitrate thus formed, is readily assimilated by the algae, and enters the
natural food web. The reservoir acts as a ‘sun-lit rumen’, and is referred
to as a ‘green-lung’, converting the organic wastes into single cell
protein. Algae produced in the process
enter the food web, encouraging secondary productivity (e.g. zooplankton),
which supplements the diet of the fish.
Adding water to the fish farm is only required to
compensate against losses due to seepage, evaporation and operational uses.
If you are ready to consider large scale fish farm, using the 'green-water'
re-circulation system,
check out our
Rapid Evaluation Program.
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