Tilapias are euryhaline and grow well in brackish and salt waters. T. mossambica and T. zillii can grow even in hypersaline waters above 42 ppt. The hybrid red tilapia seem to grow best in brackish- and sea-water environments. Species like T. aurea and T. zillii do not appear to breed in high salinities, but T. mossambica reproduce at a salinity as high as 49ppt (Popper and Lichatovich, 1975).
The most common and widely practised system of culture of tilapia is in earthen ponds and similar impoundments (fig. 20.2). As the species can survive in a restricted space, all sizes of ponds have been used, including those measuring less than 100 m2. In pond culture, attempts have been made to control overpopulation by stocking a certain number of predators (2–10 per cent of the stock), such as Hemichromisfasciatus, Lates niloticus, Clarias lazera, Micropterus salmoides, Channa striata and Cichla ocellaris. In brackish- and salt-water ponds, Elops hawaiensis and Dicentrarchus spp. have beenused as predators. In order to reduce breeding and increase production, mono-sex culture of males is carried out in a number of tilapia farms. The techniques of separating the sexes, or producing mono-sex stocks by hybridization or by sex-reversal, have not been perfected to the extent necessary to ensure the complete absence of female fish. A few female fish in the ponds can cause uncontrolled breeding.
In many areas, tilapias are produced mainly by polyculture. They have been used as a compatible species with a number of fresh-water fish, including carps, grey mullets, Clariaslazera, Heterotis niloticus and the Amazoniancharacid tambaqui (Colossoma macropomum).
Intensive monoculture of tilapia in indoor tanks is carried out in colder climates, as in China, using warm water during the winter season. Over-wintering of fry during the cold season and stocking in open ponds during the spring is also a common practice in temperate regions. The economic viability of these systems depends very much on the local market value of the species.
Cage culture of tilapia in both fresh and salt water has received considerable attention, not only for more intensive production, but also as a means of controlling wild spawning and over-population. Although in many areas it is still on an experimental or pilot scale only, there are some successful commercial operations, as for example in the Philippines and Costa Rica (fig. 20.3). Pen culture of tilapia in open waters of lakes is practised in the Philippines. Tank and raceway culture are also done on a very limited scale, for producing marketable fish (fig. 20.4) or bait fish.
In some of the countries of Southeast Asia, especially in the Philippines and Thailand, rice-field culture of tilapia is practised on an appreciable scale. To obtain marketable fish within the short period of rice cultivation or between crops, mono-sex culture has to be adopted. Tilapias have also figured as important species in integrated animal and fish farming systems in several Asian and some African countries.
Stocking in open waters has been carried out in a few countries to enhance or develop commercial fisheries. A notable success is the development of self-sustaining stocks in lakes and reservoirs in Sri Lanka and in Lake Kinneret (Tiberius) in Israel. Stocking has also been undertaken in lakes or reservoirs in East Africa (Kenya, Tanzania, Uganda, Rwanda, Zambia, Zimbabwe, etc.) and in central Florida (USA).
stocking of conservation dams with tilapias was a common practice in Central
East African countries, and lately Israel has adopted stocking in irrigation
reservoirs of 15–24 ha area (Sarig, 1983).
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