International Journal of Aquaculture, 2025, Vol.15, No.1, 21-28 http://www.aquapublisher.com/index.php/ija 22 sampling site. Three mitochondrial DNA markers were used to evaluate population structural differences between these three populations (Soliman et al., 2017), and the results showed that they had differences in population structure and genetic diversity. The research team of Jiang Bingjie selected Nile tilapia (Oreochromis niloticus), Oreochromis (O. aureus), Mozambique tilapia (O. mossambicus), and GIFT as the research subjects. The neutral test Tajima’s D value showed that the population size expanded after experiencing bottleneck effects and/or purification selection, andOreochromis had the lowest genetic diversity (Jiang et al., 2019). 2.2 Genetic characteristics of tilapia strains in Asia Tilapia has experienced extensive introduction and breeding in Asia. The tilapia breeding industry in Asia is huge in scale, diverse in varieties, and its genetic characteristics are affected by various factors such as the source of introduction, breeding methods and breeding strategies. Research experts surveyed important breeding strains from the Philippines and Africa, and used SNP array data and Poolseq SNP to characterize the population structure of these samples (Barría et al., 2023). They observed the largest gap between Asian and African populations, and the mixing degree of Asian populations was higher than that of African populations, and determined that the SNP array data could successfully parse the relationship between different Nile tilapia populations. Poolseq data identified genomic regions with high differentiation levels between GIFTw and other populations. Gene ontology terms associated with mesodermal development are significantly abundant in genes located in these regions. In pairwise comparisons between GIFTw and all other populations, there was a genetic difference in one region on chromosome Oni06. 2.3 Genetic structural characteristics of tilapia population on the American continent The tilapia population on the American continent mainly originates from African original species. After long-term trans-ocean introduction, settlement and breeding processes, it has formed unique genetic structural characteristics. Studies have shown that multiple introduction events, interspecies hybridization, and environmental adaptation pressures have jointly shaped the genetic diversity of these populations. In terms of genetic differentiation, tilapia populations in major distribution areas such as Brazil, Mexico and the United States show significant geogenetic structures. This differentiation is not only reflected in mitochondrial DNA sequence variation, but also in the allelic frequency distribution of microsatellite sites (Nyingi et al., 2009). It is worth noting that artificial selection stress and environmental adaptation jointly drive the genetic variation of these populations, where farmed populations show obvious selection signals, while wild populations retain more original genetic characteristics (Barluenga et al., 2006). This mechanism of genetic structure formation provides an important case for understanding species adaptive evolution. 3 Genetic Clues of the History of Tilapia Domestication 3.1 Genetic evidence of origin of tilapia domestication In recent years, through genetic analysis of wild and farmed tilapia populations in various regions of Africa, people have gradually unveiled the mystery of the origin of tilapia domestication. Studies based on mitochondrial DNA and nuclear genome analysis show that the Nile River Basin and the East African lake area are likely to be the main sites for the initial domestication of tilapia (Nayfa et al., 2020). Wu Feng from Sun Yat-sen University studied the genetic and molecular markers of tilapia. Using random amplified polymorphic DNA and mitochondrial gene sequence analysis technology, the genetic variation of nuclear genes and extranuclear genes was detected respectively. In the UPGMA and NJ phylogeny trees constructed by mitochondrial genes, red tilapia and Honalong tilapia first gathered together, then formed sister branches with the Mozambique matriline, and then clustered with the Nile tilapia matriline; Oriya tilapia is located at the bottom of the phylogeny tree. 3.2 Effects of early domestication events on population genetic structure The bottleneck effect during early domestication significantly reduced the genetic diversity of some populations. After genetic analysis of Oreochromis niloticus, it was found that the allelic richness and heterozygosity of breeding populations were significantly lower than that of wild populations, which was related to the fact that a few individuals were selected as breeding populations during domestication. Anthropogenic selection stress leads
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