International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.3, 123-133 http://ecoevopublisher.com/index.php/ijmec 124 This study will summarize the main findings and progress in the study of catfish population genetic structure and gene flow in recent years, focusing on the patterns and causes of different geographical regions, introducing the basic theories and technical development of catfish population genetics research, comparing the genetic structure and geographical patterns of representative catfish populations in Asia, Africa-South America, and Europe-North America, and also analyzing the key factors and mechanisms affecting catfish gene flow, and discussing the ecological and evolutionary significance of genetic structure and gene flow, including local adaptation, hybridization effects, and speciation. After introducing classic cases, it will look forward to the prospects of catfish population genetics research in species protection, genetic breeding, new technology application, and international cooperation. This study hopes to provide a reference for the protection and sustainable use of global catfish resources. 2 Theoretical Basis and Technical Progress of Catfish Population Genetics Research 2.1 Theoretical basis of population genetics The study of catfish population genetic structure and gene flow is based on the classical population genetics theory. According to the principles of population genetics, an ideal population should conform to the Hardy-Weinberg equilibrium when there are no selection, mutation, migration and other factors. However, various evolutionary forces in nature will break this balance, causing differences in allele frequencies between different populations. Genetic drift plays an important role in small populations, often leading to random differentiation of different populations; gene flow transmits alleles between populations through migration and hybridization, playing a role in balancing genetic variation. Common indicators for measuring the degree of population differentiation include FST value, which reflects the proportion of inter-population variation in total variation. When FST is close to 0, it means that there is no obvious differentiation between populations and frequent gene exchange. A higher FST value means that gene flow is limited and the population is highly differentiated (Sunde et al., 2020). For example, studies on fish populations have shown that low genetic differentiation often corresponds to higher migration and gene flow, while strong differentiation indicates geographic or reproductive isolation. In addition, local adaptation can occur when gene flow is restricted: different environmental conditions drive each population to accumulate different adaptive alleles, further exacerbating the genetic structure. In contrast, high-intensity gene flow may weaken the adaptive differences between populations. 2.2 Characteristics of ecological distribution and genetic pattern of catfish Catfish mostly inhabit freshwater bodies such as rivers, lakes, and a few species enter brackish waters in estuaries. Their ecological distribution and migration ability have a direct impact on the genetic structure of the population. For example, many tropical catfish species are confined to a single basin and lack the ability to migrate long distances, which makes populations in different river systems isolated for a long time and gradually accumulates significant genetic differentiation. In Africa, some African catfish (Clarias) populations show a highly differentiated pattern between different water systems due to river separation. Popoola (2022) analyzed African pointed catfish (C. gariepinus) in three rivers in Nigeria and found that the mitochondrial haplotypes of the river populations were not shared at all, and the FST between populations was as high as 0.95, showing a strong geographical structure. In contrast, some catfish have long-distance migration behaviors or live in connected water systems, so there is frequent gene exchange between different regional populations and the genetic structure is relatively uniform (Formiga et al., 2021). For example, large migratory catfish living in the mainstream of the Amazon River in South America, such as Brachyplatystoma species, can migrate thousands of kilometers across the river basin, forming a nearly pan-dense genetic pattern. Studies have shown that the giant catfish Piramutaba (B. vaillantii) in the middle and lower reaches of the Amazon River has no significant genetic differentiation within thousands of kilometers, and all sampled populations form a single pan-mictic population with an FST of only about 0.001 4. Therefore, due to different migration abilities and habitat connectivity, different catfish species can present a continuous spectrum of genetic structure patterns from highly differentiated to basically undifferentiated, which provides ideal materials for comparative analysis.
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