International Journal of Aquaculture, 2025, Vol.15, No.3, 99-115 http://www.aquapublisher.com/index.php/ija 107 distributed in China, such as the Channa argus group and some species of the Channa argus group. The genetic diversity of these lineages is mainly concentrated in the tropical region of Southeast Asia. For example, the mitochondrial differences of Channa argus populations in various parts of Southeast Asia are very small, indicating that it may be widely and continuously distributed in the lowlands of Southeast Asia; while there is currently no record of wild Channa argus distribution in China, which reflects the differences in species composition between regions (Liu et al., 2020). Environmental factors also lead to some phenotypic differences between Southeast Asian and South China snakeheads. For example, Southeast Asian snakeheads (such as giant snakeheads) living in tropical plain waters are huge and grow rapidly, while the spotted snakeheads in the hilly areas of southern China are medium-sized and have a more static water habit. There may be a genetic basis behind these ecological differences, and clues may be found by comparing their mitochondrial genes. Preliminary genome analysis found that tropical species such as giant snakeheads have some unique amino acid substitutions in mitochondrial coding genes, which may affect their metabolic rate to adapt to high water temperature environments; while the spotted snakeheads in South China have unique repeat sequences in the control zone sequence, which may be related to the regulation of the reproductive cycle (Hsu Htoo et al., 2025). Snakeheads in different regions differ in genetic diversity and genotype composition. For example, the genetic distance between Southeast Asian snakehead species is often greater than that between Chinese snakehead species, indicating that Southeast Asia, as a differentiation center of snakeheads, has a longer evolutionary history and richer variation. 5.2 Geographic isolation and mitogenomic differentiation Geographic isolation is one of the key factors driving species genetic differentiation and the formation of new lineages. For the widespread snakehead fish, the isolation of different watersheds and climate zones has led to the gradual accumulation of mitochondrial genetic differences. In northern and southern China, the Nanling Mountains and the Yangtze River Basin are considered to be the biogeographical dividing lines: with this as the boundary, the lineage of Channa argus in the north is completely different from the lineage of Channa maculata/Channa sinensis in the south. The existence of the Nanling Mountains blocked the natural spread of snakehead to the north and south. The uplift of the region in geological history has separated the water systems of the two regions for a long time, thus giving rise to independent mitochondrial lineages (Li et al., 2023). This is supported by genetic data: the mitochondrial sequences of Channa argus and Channa maculataare quite different, but the intraspecific differences are small, which is consistent with the pattern of long-term isolation and recent expansion. In Southeast Asia, there is also lineage differentiation caused by isolation of rivers and mountains. For example, the Irrawaddy River in Myanmar and the river system of the Malay Peninsula have different populations of snakehead, and although they are relatively close geographically, their mitochondrial lineages are almost not shared due to the independence of the water system. Even the same species of Channa striata (C. striata) shows obvious genetic structure between the Indian subcontinent, Southeast Asian mainland and Sunda Islands, corresponding to the role of paleogeographic barriers such as the Indo-Myanmar Mountains and the Sunda land bridge. These isolation events can usually be traced back to the rise and fall of sea levels and changes in river networks in the Pleistocene. For example, when the Sunda shelf was exposed during the glacial retreat, South China was connected to the Southeast Asian mainland, and species exchange may have occurred at one time; while the interglacial transgression blocked the connection, leading to isolation and differentiation. In the Yunnan Plateau in southwest China, the complex terrain and water system also nurtured the genetic diversity of the genus Snakehead. Different mitochondrial branches of small Channa such as the broad-headed Channa were found in the separated water systems such as the Lancang River and the upper reaches of the Pearl River, which may represent local lineages formed by geographical isolation. For example, the mitochondrial sequences of the broad-headed Channa population in Guangxi and the population in Xishuangbanna, Yunnan are significantly different, and are considered to be different evolutionary lineages, and their differentiation may be related to the barrier of the Ailao Mountains (Zhang et al., 2020).
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