International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.3, 144-152 http://ecoevopublisher.com/index.php/ijmec 148 of snakehead fish is related to geological and climate changes. During the Miocene period, small snakehead fish were particularly active. Against the background of frequent land and sea alternation in Southeast Asia, they underwent significant adaptive evolution (Prazdnikov, 2023). As sea levels rose and fell, land bridges appeared and disappeared. This broke up the fish's habitats. Separate groups of fish then evolved differently in isolated mountain and island areas. The climate oscillations of the Quaternary glacial interglacial cycle have also shaped the distribution pattern of existing species of moon snakehead. The genetic structure of the C. gachua population in the Indochinese Peninsula clearly reflects the water system isolation events caused by historical sea level changes (Wang et al., 2021). The species differentiation of the moon snakehead in the Indian subcontinent may have responded to regional geomorphological evolution, including the uplift process of the Deccan Plateau and the formation of the Ganges Brahmaputra River system (Böhme, 2004; Adamson et al., 2010). These geological activities create necessary isolation conditions for species differentiation by altering water system connectivity. 4 Adaptive Evolutionary Characteristics Revealed by Snakehead Genome Data 4.1 Genomic characteristics of representative Snakehead species In the past few years, studies on snakehead fish genomes have helped scientists better understand how these fish evolved. Thanks to new sequencing tools, researchers have now completed the genome sequencing and assembly of several well-known snakehead species (Han et al., 2025; Htoo et al., 2015). The findings show that the genome size of snakehead fish is somewhere in the middle-not too big or too small. When comparing their DNA with that of other freshwater fish, both similarities and differences were found. For example, snakeheads have chromosome structures that are quite similar to goldfish and betta fish (Ou et al., 2021; Andrews et al., 2023). But in certain small parts of the genome, some key changes stand out. Gene families like olfactory receptors and heat shock proteins are much larger in snakeheads, showing that these areas have expanded more in their DNA (Huang et al., 2022). 4.2 Genes related to oxygen deficiency and hypoxia adaptation One of the most acclaimed adaptive features of the blackfish genus is its tolerance to low oxygen environments and air breathing ability. This adaptability is also reflected at the genomic level. There is a correlation between the low oxygen tolerance of different fish species and their metabolic preferences: fish that tend to use fat as the main energy source for metabolism are less tolerant to hypoxia, while fish that prefer glycolysis have stronger hypoxia tolerance (Sudasinghe et al., 2020). The genomic basis for the adaptation of black fish to low oxygen can be summarized as: achieving efficient oxygen supply and low oxygen consumption through genetic modification of organ structure and metabolic physiology. On the one hand, it evolved auxiliary respiratory organs and strengthened them in angiogenesis and oxygen sensing molecular pathways (involving genes such as HIF/VEGF); On the other hand, adjusting metabolic patterns and oxygen carrier functions (involving Hb multi genes and metabolic enzyme genes) to maintain life activities during hypoxia. These imprints of adaptation on the genome include the expansion of related gene families, changes in regulatory sequences, and adaptive mutations at key protein sites (Rüber et al., 2020; Laskar et al., 2023)。 4.3 Immune system and adaptation to environmental stress Snakehead fish have a wide distribution, inhabiting environments ranging from clear streams to muddy rice paddies, and are exposed to a variety of pathogens and environmental stressors. This may have led to the evolution of unique adaptive traits in their immune system. Snakehead fish also perform well in acquired immunity. For example, studies have found that snakehead fish infection with snakehead herpes virus (SHVV), an invasive aquatic virus, induces a strong type I interferon response and expression of antiviral proteins (Cao et al., 2021). The adaptive evolution of the snakehead immune system is primarily manifested in: expanding the range of pathogen recognition and response through gene duplication and functional enhancement (expansion of innate immune receptors such as TLRs, and increased activity of the interferon pathway), and adapting to changing environments through changes in gene regulation (rhythmic regulation and stress induction of immune gene expression). This allows snakehead to thrive in pathogen-laden swamps and ponds without experiencing disease outbreaks, and also allows them to rapidly mobilize immunity and maintain homeostasis during sudden environmental changes (Cao et al., 2021; Ou et al., 2021).
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