International Journal of Aquaculture, 2025, Vol.15, No.3, 135-148 http://www.aquapublisher.com/index.php/ija 141 5.2 Hybrid breeding strategies and gene flow risks Hybrid breeding is a common strategy in tilapia modification, especially for binding to excellent traits of different species or lines. However, gene flow from hybridization can also pose ecological and genetic risks. Different species within the genus tilapia have a high degree of proximity and can produce fertile hybrid offspring. For example, in order to improve cold resistance, Olia tilapia (cold-resistant) and Nile tilapia (fast-growing) are often used to hybridize. The obtained Oni hybrid generation has both parental advantages, and both survival rate and growth performance at lower temperatures are better than those of purebreds. However, if these hybrid offspring escape into the wild and mate with local wild tilapia populations, it may introduce exogenous genes to affect the purity of the local species' gene bank, thereby changing the adaptability of the original population. In actual cases, the hybridization of Mozambique tilapia (O. mossambicus) and Nile tilapia was widely used to breed red tilapia, but its escape caused hybrid populations to appear in waters of many countries, causing genetic erosion to indigenous Mozambique tilapia (Oreochromis mossambicus). In addition, hybridization may also cause ecological invasion problems: if hybrid progeny is more environmentally adaptable than the parent, it may spread faster, aggravate the risk of foreign invasion. Therefore, the pros and cons need to be weighed in the application of hybrid breeding strategies. 5.3 Integration and localization adaptation between local and imported products During the promotion of tilapia fish farming, countries often hybridize or breed and integrate the introduced improved varieties with local original varieties to obtain varieties that are adapted to the local environment and have excellent performance. This localization adaptation process is very important for the long-term development of the aquaculture industry. The imported strain usually has the advantages of fast growth, but direct transplantation to a new environment may cause disagreement in the water and soil, such as lack of resistance to local pathogens or inadequate to local feed and water quality conditions. By hybridizing with local lines, the excellent traits of the introduced lines can be combined with the characteristics of the local lines' long-term adaptation. After the introduction of the gimot tilapia into the Philippines, it crossed with locally cultivated strains and cultivated the "Genomar Supreme Tilapia" (GST) strain. It is reported that its production performance in Philippine waters is better than that in pure gimot gimot and has a higher survival rate (Ansah et al., 2014). In Guangdong, China, researchers hybridized the Jifu strain with the local "pioneer" strain, and the survival rate of the obtained offspring in the low-temperature season was significantly improved, while maintaining the rapid growth characteristics (Malik et al., 2014). This localized breeding takes into account local low temperatures and epidemic bacteria in winter and spring, and enhances the adaptability of the strain. In Egypt and other places, it is also common to cross local Nile tilapia with imported GIFT tilapia, which increases yield to a certain extent, but at the same time leads to gene confusion in wild populations, causing concerns about the loss of genetic diversity. To this end, it is suggested that when integrating the strain, the reinforcing and other methods should be used as much as possible to make the local germplasm account for the main share to maintain a high degree of adaptation to the local environment. In addition, a complete breeding system for breeding of good varieties should be established to prevent blind hybridization between introduced lines and local lines from being blindly mixed without planning, thereby avoiding the problems of germplasm degradation or instability. Practice has proved that the strains that have been selected systematically locally perform more stably in commercial breeding. 6 Case Analysis of the Expansion of Tilapia Industry in Typical Countries 6.1 China: Development of suitable and localized varieties in multi-ecological zones China is a major tilapia breeding country, and its industrial expansion reflects the characteristics of multi-ecological zone development and localization of strains. The South China region (Guangdong, Guangxi, Hainan) located in the subtropical region has a warm climate and vast waters. Since the 1990s, tilapia farming has developed rapidly. In these areas, tilapia is widely used in different ecological farming models: for example, the Pearl River Delta region stocks tilapia in rice fields and lotus root ponds, and rice-fish symbiosis is implemented to improve comprehensive benefits; cage farming is developed in the main stream and reservoir of the Pearl River to obtain high yields (Sifa et al., 2008). At the same time, China is actively developing some non-traditional breeding areas in central and southwest China. For example, Yunnan and other southwestern plateau areas use hot
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