International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.3, 123-133 http://ecoevopublisher.com/index.php/ijmec 125 2.3 Development, evolution and application of research technology The technical means used in catfish population genetics research have undergone a development process from traditional markers to high-throughput genomic means. Early studies often used biochemical markers such as isozymes and electrophoretic proteins and molecular markers such as random amplified polymorphic DNA (RAPD) and simple sequence repeats (SSR, i.e., microsatellites) to assess genetic variation. However, RAPD and early molecular markers have limitations in repeatability and information content. Entering the 21st century, a large number of co-dominant, highly polymorphic microsatellite markers have gradually become the main force in fish population genetic research. Many studies on catfish have constructed microsatellite primers and analyzed population structure. For example, Kim et al. (2020) used microsatellites to compare the genetic variation of wild and farmed populations of Far Eastern catfish (Silurus asotus) in South Korea, and found that the allele richness of farmed populations was slightly lower than that of wild populations, but the overall genetic diversity was still high, and the genetic differentiation between populations was very weak. With the development of second-generation sequencing and third-generation sequencing, whole-genome scanning of SNP (single nucleotide polymorphism) markers has become a trend (Sunde et al., 2020). For non-model catfish, commonly used methods include RAD-seq (restriction fragment associated sequencing) and its improved methods, simplified genome sequencing technologies such as DArT-seq, and complete whole genome resequencing. For example, Vietnamese and Australian scholars collaborated to use DArT-seq technology to conduct population genome analysis of wild and farmed striped catfish (i.e., Pangasianodon hypophthalmus) in the lower Mekong River. Waldbieser et al. (2023) published high-quality reference genomes of North American channel catfish (Ictalurus punctatus) and blue catfish (I. furcatus), and constructed chromosome-level reference sequences for these two important farmed catfish. The abundance of genomic resources has greatly promoted the depth of catfish genetic research. For example, through the analysis of the whole genome and pedigree of channel catfish, researchers recently discovered that this species has a unique paternal monoallelic sex determination mechanism, that is, the expression of a single paternal allele determines sex. This discovery refreshes people's understanding of the sex determination method of bony fish (Wang et al., 2022). In addition, emerging gene editing technologies have also begun to be tried in catfish, such as CRISPR/Cas9 knockout experiments on catfish sex-related genes. 3 Geographical Patterns of Genetic Structure of Catfish Populations Worldwide 3.1 Asia: coexistence of diverse patterns Asia is one of the regions with the highest diversity of catfish species, including a large number of species from multiple families such as Siluridae, Siluridae, and Catfish. In the basins of large Asian rivers, the genetic structure patterns of different catfish populations have both highly connected and significantly differentiated cases. Catfish in the Mekong River basin have been studied in depth. Population genome analysis of Pangasianodon hypophthalmus, also known as striped catfish, which has extremely high economic value, showed (Kim et al., 2018; Manna et al., 2021) that there are at least two genetically distinct populations of this species in the lower Mekong River: the wild population in Thailand and the population in the Cambodia-Vietnam section have obvious genetic distances, which is speculated to be related to geographical barriers. Interestingly, the wild population in Thailand has the highest genetic diversity, while some wild populations in Cambodia and Vietnam have relatively low genetic diversity, which may be related to the differences in the history of fishery development and aquaculture release in different river sections. Another Mekong catfish, Pangasius krempfi, is a brackish-water tolerant catfish that can migrate to the sea. Mitochondrial control region analysis found that although this species did not show geographically separated genetic differentiation in different sections of the Mekong River, there were three genetic lineages (haplotype groups) coexisting in various places (Duong et al., 2023). In contrast, some catfish with a more scattered distribution in Asia and limited migration capacity showed significant local differentiation. For example, the Magur catfish (also known as the Indian bighead catfish, Clarias magur), which is endemic to the Indian subcontinent, has obvious genetic differentiation among populations in different regions because it inhabits river wetlands and has a small range of activity. The study also found that the overall genetic diversity of the Magur catfish is low, reflecting that its wild population has been reduced due to habitat destruction and overfishing, and
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