International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.4, 153-162 http://ecoevopublisher.com/index.php/ijmec 15 8 4.3 Genetic adaptation and rapid expansion capacity Whether black fish can successfully expand in the invasive area depends not only on the number of initially introduced individuals and their biological characteristics, but also closely related to their genetic adaptation process (Bock et al., 2016). When an invasive species enters a new environment, it needs to face different climatic, hydrological and biological factor pressures. If its population has sufficient genetic variation, it is more likely to quickly adapt to the new environment through natural selection and thus achieve expansion (Cristescu, 2016). The genomic characteristics of black fish (such as polyploid or gene replication) and abundant natural variations provide potential fitness advantages for them (Conte-Grand et al., 2017). When these fish have established a firm foothold in a new environment, they often prepare for further expansion through the preservation of genetic diversity or even evolution (Tepolt, 2015). In the future, through means such as comparative genomics and common garden experiments, the adaptive evolution mechanism during the invasion of black fish can be understood more deeply (Bock et al., 2016). This is of great significance for predicting its spread trend and formulating control strategies. 5 Regional Case Analysis 5.1 Population differentiation and adaptability in Asian Origin The native habitat of Asia is the region with the highest species diversity and genetic diversity of the genus Hyacinthus. The populations in various regions have formed obvious differentiation patterns during long-term evolution and have shown high adaptability to their respective habitats (Conte-Grand et al., 2017). In China, different species and populations of black fish correspond to diverse ecological environments: northern black fish adapt to the cold rivers and lakes in Northeast China and can survive in frozen water bodies in winter. The spotted black fish in South China can tolerate high temperature and low oxygen, and often inhabits rice fields and swamps where only residual water remains after drying up in summer (Harrington et al., 2022). The black fish populations native to Asia are often isolated from each other due to geographical barriers, but human activities are gradually breaking this isolation. For instance, the black fish in the north and south of China were originally separated from the subtropical population in the Yangtze River Basin and the temperate population north of the Yellow River. However, due to aquaculture and water diversion projects, nowadays in some areas, two different black fish species coexist or even live together. Attention needs to be paid to their ecological competition and genetic hybridization (Yan et al., 2018). In the native Asian environment, black fish populations usually co-evolve with local natural enemies, prey and competitors, and the ecological relationship is relatively balanced (Duong et al., 2019). 5.2 Genetic characteristics and spread patterns of invasive black fish in North America North America, especially the eastern part of the United States, has been a hotspot for black fish invasion in the past two decades. Among them, the spread of northern black fish (Channa argus) is particularly remarkable (Wegleitner et al., 2016). The first record of black fish colonization in the United States occurred in Maryland in 2002. After a failed small-scale clearance, the species rapidly spread along the Potomac River and entered rivers in adjacent states such as Virginia (Odenkirk and Isel, 2016). Since then, breeding populations have also been successively discovered in the Hudson River Basin of New York State, the Delaware River Basin of Pennsylvania and other places, indicating that the northern black fish has blossomed in multiple locations along the east coast of the United States, and there are significant genetic structural differences among the sampled populations (Figure 2) (Wegleitner et al., 2016). The North American black fish diffusion model, in addition to human multi-point distribution, also demonstrates a certain natural diffusion capacity. Taking the Potomac River population as an example, studies have monitored that it migrated approximately 20 kilometers upstream from the tidal freshwater area between 2004 and 2014 and entered multiple tributaries. The population size has grown exponentially and has accounted for a significant proportion in local catches (Odenkirk and Isel, 2016). However, interestingly, some studies have found that the impact of the invasion of northern blackfish on local fish communities may be lower than expected. The analysis of the downstream fishery data of Potomac by Love and Newhard (2012) shows that ten years after the large-scale
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