As the world faces the challenges of climate change and population growth, the outlook for global food security encounters unprecedented threats. Rising temperatures and altered ocean conditions are profoundly impacting aquatic ecosystems, with fish aquaculture particularly vulnerable to the effects of thermal stress.
A scientific review published by researchers from the Catholic University of Temuco, the University of Coimbra, the Autonomous University of Chile, the University of Barcelona, and the University of La Frontera delves into the neuroendocrine and molecular mechanisms underlying fish responses to thermal stress, highlighting the importance of skeletal muscle and liver tissues in mediating physiological adaptations.
A “Boiling” Ocean
The rise in sea temperatures, a direct consequence of climate change, poses a serious challenge for the aquaculture industry. Warmer waters create ideal conditions for the proliferation of harmful algal blooms and the spread of diseases, endangering the health and survival of farmed fish.
Additionally, warmer water temperatures can deplete oxygen levels, further stressing aquatic organisms.
As ectothermic organisms, fish depend on their external environment to regulate body temperature. Exposure to elevated temperatures can trigger a physiological stress response, affecting various aspects of their biology. This includes alterations in growth, reproduction, and immune function.
The Delicate Balance of Fish Physiology
Like all organisms, fish have developed complex physiological mechanisms to adapt to environmental changes. However, the increasing frequency and intensity of thermal stress events can disrupt these delicate balances.
The hypothalamus-pituitary-interrenal (HPI) axis plays a crucial role in regulating stress responses in fish, where cortisol and catecholamines act as key mediators. These hormones influence energy metabolism and stress adaptation, enabling fish to respond to changing environmental conditions.
When fish are exposed to elevated temperatures, the HPI axis is activated, leading to the release of stress hormones such as cortisol and catecholamines. These hormones, in turn, trigger a cascade of physiological responses, including changes in metabolism, immune function, and growth.
Molecular Mechanisms of Thermal Stress Response
According to the study published in Aquaculture Reports, recent research has shed light on the molecular mechanisms underlying fish responses to thermal stress. Key tissues, such as skeletal muscle and liver, are particularly susceptible to the effects of elevated temperatures. These tissues undergo significant molecular adaptations, including alterations in gene expression related to growth, energy metabolism, and stress response. For example, thermal stress can alter the expression of genes involved in glycolysis and oxidative phosphorylation, two essential metabolic pathways.
Moreover, the expression of genes related to hormonal signaling, such as growth hormone and insulin-like growth factors, may be affected, impacting growth and muscle development.
Key Findings
In summary, to cope with thermal stress, fish employ a complex network of molecular mechanisms, including:
- Activation of the Hypothalamus-Pituitary-Interrenal (HPI) Axis: The HPI axis plays a crucial role in regulating the stress response, mobilizing energy resources and enhancing oxygen supply to tissues.
- Heat Shock Proteins (Hsps): Hsps are essential for maintaining cellular homeostasis and protecting cells from thermal stress-induced damage.
- Metabolic Adaptations: Fish can adjust their metabolic rates to cope with elevated temperatures, altering the expression of genes involved in energy metabolism, growth, and muscle function.
Implications for the Aquaculture Industry
Understanding the physiological and molecular responses of fish to thermal stress is crucial for the sustainable development of aquaculture. By identifying the key molecular mechanisms involved, researchers can develop strategies to mitigate the negative impacts of climate change on fish health and productivity. Possible strategies include selective breeding for heat tolerance, optimizing feeding regimes, and improving water quality management.
However, the authors of the study emphasize that more needs to be understood about:
- Molecular Biomarkers: Identifying and validating new molecular biomarkers, such as those related to growth, oxidative stress, and inflammation, can help assess fish health and welfare under thermal stress.
- mTOR/Akt Signaling Pathway: Further research on the mTOR/Akt signaling pathway could provide insights into the molecular mechanisms underlying cellular responses to thermal stress.
- miRNA: Exploring the role of miRNAs in regulating stress response pathways may lead to the development of new strategies to enhance fish thermotolerance.
Conclusion
In conclusion, this scientific review provides a comprehensive overview of the neuroendocrine and molecular mechanisms underlying fish responses to thermal stress. By highlighting the importance of skeletal muscle and liver tissues in mediating physiological adaptations, we can better understand the impact of thermal stress on fish aquaculture and develop effective strategies to ensure the long-term sustainability of this essential food source.
As climate change continues to intensify, it is imperative to invest in research and innovation to ensure the long-term sustainability of aquaculture. Addressing the challenges posed by thermal stress and other climate-related factors can help safeguard global food security.
The study was funded by the National Research and Development Agency of Chile, ANID, with the collaboration of the Catholic University of Temuco.
Contact
Alberto Sáez-Arteaga
Centro de Investigación, Innovación y Creación UCT (CIIC-UCT), Universidad Católica de Temuco
Temuco, Chile.
Email: alberto.saez@uct.cl
Reference (open access)
Sáez-Arteaga, A., Viegas, I., Palma, M., Dantagnan, P., Valdebenito, I., Figueroa Villalobos, E., Hernández, A., Guerrero-Jiménez, J., Metón, I., & Heyser, C. (2024). Impact of increasing temperatures on neuroendocrine and molecular responses of skeletal muscle and liver in fish: A comprehensive review. Aquaculture Reports, 39, 102448. https://doi.org/10.1016/j.aqrep.2024.102448
