Tank and raceway culture
The
interest in tank and raceway culture of tilapia originated with experiments of
determine the suitability of tilapia as bait fish for tuna. In experimental
work in Hawaii, it was demonstrated that spawning and fry rearing could be
carried out in raceway-type 4500 l tanks (6m x 0.9 m and 0.9 m deep). Later
efforts in tank farming were mostly for environmental rehabilitation, as in the
case of the Baobab Farm near Mombasa, Kenya, where large lime-stone quarries
were created by the excavation of coral scrublands for cement manufacture. In
the Baobab Farm, the fry are stocked in a two-tier raceway system, at the rate
of 1000–2000 per m3. They are regularly graded and the fast-growing
ones, comprising 70–90 per cent males, are introduced into the lower tier of
the race-ways. Fingerlings weighing 50–75 g are transferred to a series of
circular production tanks of about 20 m3 capacity and fed regularly
on palletized feed containing 20–35 per cent protein. A continuous water flow
rate of 0.5– 1.0 l/min per kg is maintained in the tanks, which is adequate to
provide the oxygen requirements and to flush out waste products. The stocking
rate is 200–500 per m3. In about 3 months, around 70 per cent of the
stock reach about 250 g and can be marketed. Each tank can produce four crops
per year with yields between 100 and 200 kg/m3 per year. According to
Balarin and Haller (1983) the most economic unit under Kenyan conditions is a
75–100 ton facility, with the expected return on capital of nearly 25 per cent
of total investment.
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