Hypoxia-induced physiological responses in fish: From organism to tissue to molecular levels

Dissolved oxygen (DO) in water bodies is a prerequisite for fish survival and plays a crucial role in fish growth, development, and physiological processes. However, with increasing eutrophication, greenhouse effects, and extreme weather conditions, DO levels in aquatic environments often become lower than normal. This leads to stress in fish, causing them to exhibit escape behavior, inhibits their growth and development, and causes tissue damage. Moreover, oxidative stress, decreased immune function, and altered metabolism have been observed. Severe hypoxia can cause massive fish mortality, resulting in significant economic losses to the aquaculture industry. In response to hypoxia, fish exhibit a series of behavioral and physiological changes that are self-protective mechanisms formed through long-term evolution. This review summarizes the effects of hypoxic stress on fish, including the asphyxiation point, behavior, growth and reproduction, tissue structure, physiological and biochemical processes, and regulation of gene expression. Furthermore, future research directions are discussed to provide new insights and references.