الفهرس 
Review of LiteratureOnly 14 pages are availabe for public view
 |  | from | 146 |  |  |
| | | from | 146 | | |
Abstract
CHAPTER 1
INTRODUCTION
Tilapias belong to the family Cichlidae which is widely distributed in Africa, the Middle East, South and Central America, southern India and Sri Lanka. It contains approximately 1300 species, of which approximately 150 can be called tilapia. Tilapia is perciform fish that originated in Africa. They have adapted to diverse habitats: permanent and temporary rivers, rivers with rapids, large equatorial lakes, tropical and subtropical rivers, open and closed estuaries, lagoons, swampy lakes, deep lakes and coastal brackish lakes (Trewavas, 1983). The most commercially important tilapia genera are : Oreochromis, Tilapia and Sarotherodon. The genus Oreochromis is the largest, with approximately 79 species, followed by Tilapia with approximately 41 species and the genus Sarotherodon with approximately 10 species. The rapid growth of tilapia, their resistance to poor water quality, ability to grow under sub optimal nutritional condition, and high fecundity all make them suited for aquaculture (Amal et al., 2005; Robert, 2003).
Development of tilapia hybrids has been pursued to incorporate desirable traits into hybrids and hybrid- based verities. The development of hybrid - based tilapia varieties is an important step toward increasing production and marketability of tilapia (Lutz, 2001). By combing the beneficial traits found in several tilapia species into hybrids, scientists and producers create fish that grow faster and are less expensive to produce. These efforts have had varying degrees of success (Rakocy et al., 1993). Some hybrid – based varieties may exhibit traits beneficial to commercial scale farming such as cold or salinity tolerance (Robert, 2003). And the progeny highly tolerant to saline condition might be produced through hybridization and other genetic manipulation techniques. The main reasons for genetic manipulation of species used in aquaculture are all directly connected to improve output / input ratios. Genetic manipulations used are :-
• To enhance growth and /or efficiency of feed conversion.
• To enhance commercially significant flesh characteristics.
• To control reproduction activity and/or sexual phenotype.
• To increase resistance of species to pathogens / parasites.
• To increase tolerance to environmental variables such as temperature and salinity.
• To modify behavior, e.g. aggression.
• To control fertility and/or viability.
Transgenic fish technique is one of the attempts to increase the production of economically important fish for human consumption. The application of gene transfer is used to increase growth rate, tolerance to cold water, disease resistance and salinity tolerance. In this connection Devlin et al. (1994) reported that, transgenic fishes with defined performance will potentially be beneficial to aquaculture by providing more effective means of enhancing performance than traditional breeding methods.
Moreover, Guillen et al. (1999) reported that, modern marine biotechnology have permitted the generation of new strains of economically important fish species through the
performance and therefore constitute a better alternative for aquaculture programs. Also transgenic tilapia line with accelerated growth was
obtained. However, before national authorities required introducing this line into Cuban aquaculture, environmental and food safety assessment experiments were performed to evaluate the behavior of transgenic tilapia in comparison to wild tilapia as a way to assess the environmental impact of introducing transgenic tilapia into Cuban aquaculture. Studies were also conducted to evaluate, according to the principle of substantial equivalence, the safety of consuming transgenic tilapia that had a lower feeding motivation and dominance status than control. Food safety assessment indicated that tilapia growth hormone has no biological activity when administered to non-human promotes. Furthermore, no effects were detected in human healthy volunteers after the consumption of transgenic tilapia. These results showed, at least under the condition found in Cuba, no environmental implications for the introduction of this transgenic tilapia as an alternative feeding source for human. These results support the culture and consumption of this transgenic tilapia.
Therefore, the present work aimed to evaluate the performance of Blue Tilapia (Oreochromis aureus), through a comparative study between inter-specific Cross-breeding with Oreochromis niloticus and introduced a fragmented purified DNA isolated from Common Carp, (Cyprinus carpio) and Nile Tilapia, (O. niloticus) into gonads of O. aureus (males and females). In addition the effect of two breeding methods on growth performance, body composition, feed utilization and DNA fingerprinting of O. aureus were carried out.