A recirculating system and a pond farm are at opposite ends of the aquaculture spectrum. The sweet spot is somewhere in between.
The type of system employed in a fish production unit depends on many factors. The most crucial is the species being farmed. Almost as important, though, is the level of sophistication of the technology.
The most complex set-up is the recirculating aquaculture system (RAS), and the simplest is the pond-based system. Each has its advantages. An RAS uses and reuses a limited volume of water, has a small footprint, allows for climate control, and enables intensification (increasing the stocking rate). A pond farm offers lower risk, requires fewer skills to operate, and is less dependent on a reliable power supply.
A question of numbers
A simple tilapia RAS may comprise a number of tanks inside a hothouse tunnel. The grow-out tanks are connected to other containments that comprise the filtration needed to remove the waste products.
Such an unsophisticated set-up is for practising aquaculture as a hobby, not for commercial purposes. The maximum fish stocking density is between 5kg/ m3 and 10kg/m3 water; more than this will result in sediment accumulation, ammonia spikes and poor water quality.
If intensification is increased to commercial stocking rates (between 20kg/ m3 and 50kg/ m3), the need for sophisticated life-support technology will increase.
Or will it?
The limiting factors in intensive fish farming are availability of oxygen, and ammonia and solids removal.
Technical sophistication is not simply a function of the scale of operation, or availability of funding. Risk must be paramount in determining choice. Using an intensive system that depends on electric machinery for oxygenation, solids removal or filtration, one must assume that failure of a component is inevitable.
If this will result in stock losses, duplication is essential. In addition, staff must be competent in running and repairing such equipment.
I recommend the use of high-volume settlement units, wide but shallow grow-out tanks, and massive volume filtration. This offers greater simplicity, less risk of failure, lower running costs, and fewer sleepless nights.
How the system works when it is new is irrelevant; how it works when it is old is what really matters!
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