| Summary: | The Ob River is the largest river in Eurasia, and its ichthyofauna in the Middle Ob consists of species that inhabit not only the entire river but also the upper and lower reaches. This region faces numerous anthropogenic activities that pose a significant threat to aquatic biodiversity. Therefore, changes in fish species diversity in the Middle Ob can serve as an indicator of the overall ecosystem health. This study aims to analyze these changes and their potential causes. Materials and methods: This study presents an analytical review of the Middle Ob River ichthyofauna over the past 120 years. It assesses changes in fish species diversity and discusses various natural and anthropogenic factors. Results: The ichthyofauna of the Middle Ob basin currently includes 38 fish species from 2 classes, 9 orders, 12 families, and 30 genera. Over the past century, the number of species has increased by 27%, with 9 naturalized alien species and 1 extinct species. Additionally, there has been a significant decrease in the abundance of some commercial fish species. The ichthyofauna of the Middle Ob is influenced by hydraulic construction, pollution, overexploitation of aquatic resources (especially commercially valuable fish species), the expansion of alien species, anthropogenic alteration of the river bed, and climate change. Conclusion: While most factors affect the abundance of individual fish species, they do not significantly impact fish species diversity, with the exception of alien species and pollution.
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