International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.3, 123-133 http://ecoevopublisher.com/index.php/ijmec 126 its genetic variation has been damaged. This situation deserves great attention, and independent conservation measures need to be formulated for populations in different regions (Sahoo et al., 2021). 3.2 Africa and South America: river isolation and super migration Africa and South America are both freshwater fish diversity hotspots, with many catfish species with their own characteristics. Although the genetic patterns of catfish populations in the two continents are different, one thing in common is that the isolation of the river basin has an important impact on the genetic structure. African catfish (especially members of the Clariidae family) are often distributed in independent river and lake systems. The gene exchange between populations in different river systems has been restricted for a long time, showing significant genetic differentiation. For example, Popoola (2022) conducted mitochondrial DNA analysis on North African catfish (i.e., African pointed catfish, Clarias gariepinus) in three independent lakes/rivers in Nigeria. The results showed that the populations in each water body had a unique haplotype lineage, and the genetic distance between populations was extremely large. In addition to river basin isolation, the genetic structure of catfish populations in South America is also significantly affected by the ultra-long-distance migration behavior of these fish. The Amazon-Orinoco River basin in South America is home to a variety of giant migratory catfishes, whose migration behavior allows for gene exchange between long-distance populations in the main river channel (Figure 1) . The Amazon white catfish (Brachyplatystoma vaillantii), which belongs to the same family as the Panamerican catfish, is a representative species of the Amazon-Atlantic migration (Barthem et al., 2017). Its population along thousands of kilometers of the Amazon River has almost no genetic structure (Formiga et al., 2021). However, not all South American catfishes show such a weak structure. Some small and medium-sized catfishes are distributed in the huge Amazon basin, but their migration ability is limited or confined to tributaries, so they may have a geographical lineage structure. For example, the Medellin catfish (Pseudoplatystoma magdaleniatum) showed an overall single population before and after the damming of the Magdalena River basin in Colombia (García-Castro and Márquez, 2024). Figure 1 Several migratory giant catfish species in the Amazon basin (Brachyplatystoma, Pimelodidae) (Adopted from Barthem et al., 2017) Image caption: (A) Brachyplatystoma vaillantii; (B) Brachyplatystoma rousseauxii; (C) Brachyplatystoma platynemum; (D) Brachyplatystoma juruense; (E) Dorado migrations exploited by fishermen (Adopted from Barthem et al., 2017) 3.3 Europe and North America: invasion and localization patterns Compared to tropical regions, native catfish in Europe and North America have lower diversity and relatively shallow differentiation of population genetic structure. In Europe, native catfish are mainly European catfish (Silurus glanis, also known as river catfish or glanis catfish), whose historical distribution center is in the Danube River and Eastern European waters (Cucherousset et al., 2018; Ditcharoen et al., 2019). Since European catfish only re-spread after the glacial period, the genetic differences between modern populations are limited. Previous studies based on mitochondrial DNA have found that European catfish in Eastern European rivers have not formed obvious phylogenetic differentiation. However, in recent years, as this species has been introduced into some basins in Western Europe by humans and formed breeding populations, its genetic structure has become
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