Fish gut plasticity and its role as a potential mechanism for coping with warming and hypoxia

The fish gut plays a critical role in nutrient absorption, growth, immune response modulation, health and overall homeostasis. It also represents one of the most energetically expensive organ systems to maintain and demonstrates remarkable plasticity, including changes in morphology, function and cellular-level processes in response to environmental factors. Despite its importance and known capacity for plasticity, the role of the gut in fish responses to environmental change, such as warming and hypoxia, has been historically overlooked. For example, compared with research on the plasticity of other organ systems, such as the heart and gills, studies on how the fish gut influences whole-animal responses to stressors remain scarce. This Review addresses this disparity by highlighting the plasticity of the teleost gastrointestinal system and how this plasticity might drive responses to both long-term climate change and acute environmental fluctuations. It discusses the underlying mechanisms of gut plasticity, including cellular and molecular responses (e.g. changes in gene expression and transporter localisation), as well as structural and functional adjustments, including changes in organ size and length. This Review concludes with a call to action for targeted research aimed at advancing our understanding of fish gut plasticity and its role in fish responses to environmental change, with a specific focus on warming and hypoxia. Closing these knowledge gaps will allow scientists to better predict and mitigate the impacts of climate change on aquatic ecosystems and food production systems, such as fisheries and aquaculture, and will contribute to management action aimed at conserving marine and freshwater biodiversity.