International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.4, 153-162 http://ecoevopublisher.com/index.php/ijmec 15 6 The ornamental fish trade has risen in recent years, driving some small or brightly colored black fish into the global pet market. India is one of the centers of snakehead diversity. Its exports of live snakehead increased sixfold from 2014 to 2019, mainly to mainland China, Taiwan, and Hong Kong (Harrington et al., 2022). Among them are many newly described "rainbow black fish" species. Due to the difficulty in species identification and insufficient trade regulation, once they escape or are abandoned, they may survive and reproduce in non-native environments. Black fish can be carried by humans across natural geographical barriers through live fish transportation and market sales. The fact that northern black fish appeared almost simultaneously in several disconnected river basins in the United States suggests that it is very likely the result of multiple introduction through different channels (Wegleitner et al., 2016). In Asia, the situation where native species are artificially transplanted and spread is more common. For example, the striped black fish has been artificially brought into the Philippines, some islands in Oceania and even areas outside the Korean Peninsula (Duong et al., 2019). In addition, religious release of animals is also a potential approach. In some Asian cultures, there is a tradition of releasing live fish back into nature, which may unintentionally introduce black fish into waters that do not exist originally (Gozlan et al., 2010). 3 The Genetic Structure and Differentiation Pattern of Black Fish Populations 3.1 Research progress in molecular markers and population genetics Molecular genetic markers provide a powerful tool for analyzing the population structure and invasion and spread history of black fish. Early studies mostly employed haplotype analysis of mitochondrial DNA fragments (such as control region D-loop or COI genes) to reveal the phylogenetic geographical patterns of species and potential latent species (Conte-Grand et al., 2017). In recent years, microsatellite (short tandem repeat) and single nucleotide polymorphism (SNP) markers have been widely used in population genetics studies of black fish (Yan et al., 2014; Wegleitner et al., 2016). After the rise of high-throughput sequencing, methods such as restriction enzyme restriction site association sequencing (RAD-seq) have been used for genome scanning of black fish, obtaining thousands of SNP loci and achieving a fine characterization of the population structure (Resh et al., 2018; Resh et al., 2021). In addition, methods such as whole genome sequencing and mitochondrial genome sequencing have also begun to be applied in black fish research: Xu et al. (2023) constructed a chromosomal reference genome of northern black fish, providing valuable resources for understanding the adaptive evolution of black fish; Some scholars have determined the complete mitochondrial genomes of multiple black fish species and conducted phylogenetic analyses, clarifying the evolutionary relationships within the black fish family. 3.2 Genetic diversity and lineage division of native populations The native populations of black fish usually have high genetic diversity and obvious geographical differentiation patterns. This is partly due to the long-term evolution of the black fish species over a vast area of Asia, which has been affected by river basin isolation and climate change, resulting in different local populations. On the other hand, some traditionally classified "widespread species" may actually contain several lineages with significant genetic differences (Conte-Grand et al., 2017). Take the striped black fish (Channa striata) as an example. Studies have shown that this species can be divided into at least two major genetic lineages, east and west, within its distribution area in North Borneo. The divergence between the two corresponds to the river segregation caused by paleogeographic events (Robert et al., 2019). High genetic diversity means that the native black fish has a rich gene pool, which is conducive to its adaptation to the variable environment (Duong et al., 2019). At the same time, the existence of different lineages should be treated with caution when classifying black fish and dividing conservation units. For instance, in recent years, a variety of new black fish species have been discovered in northeastern India and Myanmar. Many individuals that were previously classified as a known population actually belong to undescribed new species (Conte-Grand et al., 2017; Harrington et al., 2022). For invasive ecology, clarifying the genetic background of native populations is helpful for tracing the sources of alien populations.
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