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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