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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.

 

Large-scale fish farming

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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