International Journal of Aquaculture, 2025, Vol.15, No.4, 175-183 http://www.aquapublisher.com/index.php/ija 179 traffic rate of migratory fish; if completely removing the dam is not feasible, building an eco-friendly fish path is a common alternative method to enable fish to bypass obstacles and continue to migrate. River channel transformation (such as filling channels, restoring bends) can reconstruct a variety of riverbed morphology and water flow environments, increasing fish hiding places and foraging sites (Hayes et al., 2023). In lakes and wetlands, dredging of polluted sediments and rebuilding the bottom terrain is also an important means to restore water cleanliness and benthic biological habitats. Many cases show that the general improvement in fish diversity and abundance of rivers and lakes after engineering intervention is a direct and significant improvement measure (Bennett, 2024). 5.2 Ecological engineering and biological restoration Ecological engineering restoration focuses on the use of natural processes to restore ecological functions, such as wetland reconstruction, vegetation restoration and artificial reef construction. Restoring wetlands and mangroves can provide fish with natural spawning and childbirth places, while improving water quality through vegetation purification (Whiterod et al., 2021). Artificial reefs (such as dropping trunks, stones or artificial structures) can simulate natural reef environments, provide fish with habitat and food opportunities, and increase local biomass. Researchers also often regulate the food network by combining the control of fish population (such as moderate clearing of nets to reduce the amount of fish at the bottom) and proliferation and release (artificial breeding of fish and release of fish) to restore the ecosystem to a stable state. In recent years, microhabitat restoration technology based on the principles of fish ecology has made progress, such as designing spatial structures according to the needs of fish migration and egg spawning, and optimizing hydrological conditions in combination with flow regulation (Wang, 2025). These ecological restoration methods are often combined with engineering methods to comprehensively improve habitat quality and have a more lasting effect. 5.3 Comprehensive management and legal protection Scientific and reasonable laws, regulations and management measures are the guarantee for the restoration of aquatic habitats. Many countries have formulated strict fishery fishing bans and water quality standards. For example, China's implementation of a ten-year fishing ban in the Yangtze River Basin has provided a policy-level protection period for the recovery of fishery resources. Through the basin master plan, the water resources management department will limit new pollution emissions, strengthen basin monitoring and cross-regional coordination, and achieve pollution control and ecological restoration from source to end. In addition, the establishment of public education and ecological compensation mechanisms can also improve the protection awareness of the whole society (Zhao et al., 2015). The internationally advocated watershed management concept of "from source to estuary" and measures such as comprehensive water resource management can effectively prevent the negative effects caused by disorderly local repair measures. Comprehensive strategies combining engineering technology, ecological methods and legal management are an effective way to restore aquatic habitats and maintain the health of fish populations. 6 The Positive Impact of Recovery on Fish Populations 6.1 Improvement of fish species diversity and population density Habitat restoration significantly improves the number and diversity of fish populations. Taking the ten-year fishing ban in the Yangtze River as an example, within only more than four years of fishing ban, the monitoring species of indigenous fish in the Yangtze River Basin increased from 308 before the fishing ban to 344, with 36 new species added. This trend shows that fish populations have strong resilience without overfishing interference (Hardison et al., 2023). Similarly, after the river barrier was removed, the migratory channels of fish along the coast were reopened, and the number of backswimming fish species increased significantly (Figure 2). For example, the WWF reported that after the demolition of old dams in Maine, the United States, the number of local migratory fish sub-adult fish jumped from thousands to millions. In lake wetland restoration projects, wetland area expansion and water quality improvement are often accompanied by rapid rebound in fish populations, indicating that the restoration of benthic food webs and habitat structures provides the basis for fish reproduction (Figure 3) (Mahoney et al., 2021).
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