Twelve tilapia species (six Oreochromis spp. ; two Sarotherodon spp. ; and four Tilapia spp. ) and one hybrid have been introduced into 30 Asian countries. Of the species introduced to Asia, O. mossambicus and O. iloticus are by far the most important from both production and scientific points of view. These species are now widely distributed in most of Asia and occur in natural and quasi-natural waters making them a part of the fish fauna of most of tropical and even sub-tropical Asian aquatic environments (4). The “red tilapia”, a hybrid between strains of O. mossambicus x O. iloticus is currently considered as important to aquaculture in Asia (5). In general, Tilapias have been introduced into over 90 countries worldwide, with a global distribution second only to common carp. Although tilapia has been associated with adverse environmental impacts, detailed analysis of the literature suggested that other factors, such as over fishing, environmental degradation from land-based activities, and changes in hydrological regime have probably been more responsible for adverse impacts. It is clear that numerous factors working together can impact biodiversity.
It is also clear that tilapias, as a group of alien species, have made a significant contribution to food production, poverty alleviation and livelihoods support in Asia and the Pacific. In spite f the wide-scale introduction into Asian waters, there is scant explicit evidence to indicate that tilapias have been overly destructive environmentally (6). Thus, Asian countries are major producers and consumers (7) Tilapia Production The current aquaculture production (2002) of tilapias is about 1. 5 million tones, the great bulk of which takes place in Asia accounting for nearly 80 percent of the total world production.
It is important to note, however, that tilapia culture in Africa and South America is also increasing. Prior to the mid-1990s, the yield of tilapia from ccounts for approximately 2. 5 times the production from capture fisheries. Tilapia aquaculture production increased from 28 000 tons to 1. 504 million tons globally from 1970 to 2002; in Asia and the Pacific, production increased from 23 000 tons to 1 . 192 million tons equivalent to an annual growth rate of 13. 2 percent and 13. 1 percent, respectively. In contrast, capture fisheries for tilapias have grown at the rate of 3. 5 percent per annum.
China alone produces nearly half of the world tilapia production followed by Egypt, Indonesia, Philippines, Thailand and Taiwan (Fig. ). Tilapias can be reared in ponds, tanks, cages and rice fields. Fig. 4 The highest ranked countries in Tilapia production Constraints of Tilapia culture Over-population due to early sexual maturity of tilapia. Cold sensitivity. Vulnerability for toxins of blue green algae in case of tilapia monoculture. Claims of invasiveness of tilapia. Suggested solutions and useful practices Production of monosex tilapia via Genetic hybridization. monosex production. Sterilization.