International Journal of Aquaculture, 2025, Vol.15, No.3, 99-115 http://www.aquapublisher.com/index.php/ija 110 etc.) and are located in the tropical-subtropical transition zone with rich biodiversity. The phylogenetic tree constructed based on the mitochondrial whole genome sequence shows that the Channa maculata samples from Guangxi and Vietnam are clustered together with almost no genetic differentiation, which supports that they belong to the same species and the same lineage. This also confirms that Guangxi and the northern part of Indochina were geographically connected (such as the Red River Basin), allowing Channa maculata to be widely distributed. The broad-headed Channa samples in Guangxi and the broad-headed Channa (or closely related species) samples in northern Vietnam also clustered into one branch, belonging to the Gachua lineage. This shows that there is a continuous distribution of the broad-headed Channa lineage in the mountain stream environment of South China and Indochina, without obvious isolation. In contrast, the situation in Yunnan is more complicated. Snakehead samples in western Yunnan (mainly Channa spp.) cluster with some samples from Thailand and Myanmar on the phylogenetic tree, but independent small branch lines also appear (Figure 2) (Tan et al., 2012; Hsu Htoo et al., 2025). For example, the Channa spp. in Xishuangbanna, Yunnan, and the Channa spp. in northern Thailand cluster into sister groups, suggesting that they were once connected through the Lancang-Mekong River system; while some snakehead samples in southeastern Yunnan (possibly Channa sinensis or its close relatives) are close to samples in southern China, indicating a connection with the Pearl River system. This reflects Yunnan's special status as a biogeographic intersection: its western water system belongs to the Southeast Asian basin, and its eastern water system belongs to the Pearl River basin in China. Therefore, the lineages of snakeheads in different regions are respectively connected to the lineages of the Indochina Peninsula or South China. Specifically, Yunnan samples can be divided into two categories on the phylogenetic tree: one is adjacent to Southeast Asian species (such as Channa fasciatus or Channa annanensis), and the other is adjacent to Chinese species (such as Channa maculata and Channa sinensis). This indicates that Yunnan has preserved Snakehead lineages from both directions, which may be the result of multiple biological migrations and isolations in history. During the glacial period, the climate of the Yunnan Plateau was cool and humid, connecting the northern and southern habitats, allowing some South China lineages to spread westward; and the expansion of the South Asian tropical forests during the interglacial period facilitated the Southeast Asian lineages to enter Yunnan from the north. 6.3 Ecological adaptations influencing lineage evolution in key habitats The evolutionary adaptation of Snakehead in different ecological environments is an important aspect of understanding its lineage formation. In typical aquatic environments (such as high-altitude mountain streams, low-oxygen swamps, cold lakes, etc.), Snakehead lineages often show special ecological and behavioral characteristics, suggesting that there are corresponding genetic adaptation mechanisms behind them. Taking the plateau mountain stream environment as an example, the members of the broad-fronted snakehead lineage living there are relatively small individuals, short life cycles, and early sexual maturity, reflecting the tendency of "r-strategy" to cope with environmental instability (Wang et al., 2023). These characteristics may be partly determined by genetics. In the mitochondrial genome of these fish, some mutations that enhance basal metabolism and reproductive rate may have been fixed, allowing them to reproduce rapidly in the resource-limited mountain stream environment. This adaptation mechanism is similar to the strategy of alpine cold-water fish to evolve higher reproductive investment to compensate for high mortality. Some black fish (such as mud snakeheads) live in swamps or rice fields with poor water quality and low dissolved oxygen, and have evolved auxiliary organs for air breathing and certain amphibious capabilities. Mitochondria play a key role in this adaptation: effective anaerobic metabolism and a lower oxygen-consuming respiratory chain may be the key to their survival. Studies have found that black snakeheads that can survive in the air have a higher tolerance to lactic acid accumulation in their blood and muscles. It is speculated that their mitochondria may have adjusted the pyruvate metabolic pathway to adapt to frequent hypoxia. This suggests that lineages such as the black snakehead may have improved mitochondrial enzyme functions, such as the Cyt b complex reducing
RkJQdWJsaXNoZXIy MjQ4ODYzNA==