International Journal of Molecular Zoology, 2025, Vol.15, No.2, 48-57 http://animalscipublisher.com/index.php/ijmz 48 Research Insight Open Access Genomic Basis and Evolutionary Adaptation Mechanisms of Hypoxia Tolerance inCatfish Baohua Dong1, Xianming Li 2 1 Institute of Life Sciences, Jiyang Colloge of Zhejiang A&F University, Zhuji, 311800, Zhejiang, China 2 Aquatic Biology Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China Corresponding author: xianming.li@cuixi.org International Journal of Molecular Zoology, 2025, Vol.15, No.2 doi: 10.5376/ijmz.2025.15.0006 Received: 10 Jan., 2025 Accepted: 15 Feb., 2025 Published: 12 Mar., 2025 Copyright © 2025 Dong and Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Dong B.H., and Li X.M., 2025, Genomic basis and evolutionary adaptation mechanisms of hypoxia tolerance in catfish, International Journal of Molecular Zoology, 15(2): 48-57 (doi: 10.5376/ijmz.2025.15.0006) Abstract This study analyzes the physiological adaptation characteristics, genomic basis, and evolutionary mechanisms of catfish hypoxia tolerance, and summarizes the recent research progress in functional genomics. The study finds that catfish show unique behavioral adjustments (such as reduced activity and surface breathing) and respiratory system modifications under hypoxic conditions, and adapt to oxygen deficiency by reducing metabolic rate and strengthening anaerobic metabolism. At the genomic level, catfish hypoxia tolerance involves the expansion or regulatory optimization of core hypoxia signaling pathway genes such as HIF, the adaptation of energy metabolism-related genes, the efficient mobilization of antioxidant and stress response genes, and evolutionary changes in the hemoglobin gene family. This paper also lists typical examples of hypoxia tolerance evolution in catfish species, such as channel catfish and other related species, and discusses the prospects of applying hypoxia-tolerant genetic traits to aquaculture breeding, as well as strategies to enhance the resilience of freshwater fisheries in the context of climate change. This study deepens the understanding of the genomic basis and evolutionary mechanisms of catfish hypoxia tolerance, which is of great significance for aquaculture strain improvement and research on fish adaptive evolution. Keywords Catfish; Hypoxia tolerance; HIF pathway; Genomic adaptation; Evolutionary mechanism; Aquaculture breeding 1 Introduction In recent decades, due to factors such as climate warming and eutrophication, the hypoxic areas of water bodies around the world (dissolved oxygen below 2 mg/L) have expanded significantly. Hypoxia is considered to be an important stressor affecting aquatic ecosystems, which can have adverse effects on the behavior, development, survival and reproduction of fish (Murphy and Rees, 2024). When the dissolved oxygen content in water drops below the threshold, many fish show phenomena such as decreased swimming ability, reduced feeding, restricted habitats and even large-scale deaths. For example, hypoxic "dead zones" in oceans and freshwaters have posed a serious threat to fishery resources (Diaz and Rosenberg, 2008; Bailey et al., 2020). Faced with hypoxic stress, different fish have evolved a variety of tolerance strategies, including behavioral avoidance or respiratory adjustments, physiological changes in ventilation and circulatory systems, and biochemical metabolic reprogramming. Studying the hypoxic adaptation mechanism of fish is not only of great significance to ecology, but also provides a scientific basis for aquaculture to cope with environmental changes (Wang et al., 2023). Catfishes in the Siluriformes family are known for their high ecological diversity and tolerance to harsh environments. Many of these species inhabit warm, slow-flowing, and even severely hypoxic waters, such as swamps, rice fields, and mud ponds. The ecological success of catfishes is largely due to their outstanding tolerance to low oxygen: they are often observed to be able to maintain basic life activities when dissolved oxygen is extremely low, and some species are even able to breathe air. For example, African catfish (Clarias gariepinus) have auxiliary respiratory organs that allow them to breathe air directly when wetlands are hypoxic, thus surviving in semi-terrestrial environments. Another example is the common farmed species, channel catfish (Ictalurus punctatus), which has no specialized respiratory organs but has a strong tolerance to periodic hypoxia and can survive when dissolved oxygen drops sharply in ponds at night. Field trials have shown that catfish can still feed and grow in water bodies with dissolved oxygen levels of only about 20% of normal levels. This adaptability
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