Acclimatization and antioxidants help rainbow trout adapt to heat waves

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By Milthon Lujan

Rainbow trout. Source: Hero
Rainbow trout. Source: Hero

Climate change is wreaking havoc on our water resources, impacting temperature, salinity, oxygen levels, and acidity. This can be devastating for aquaculture, especially for cold-water fish like rainbow trout. In this way, rising water temperatures pose a significant threat, as they weaken the immune system and even cause death.

A new study by researchers from Shiraz University (Iran) explores two promising strategies to help trout cope with heat stress: acclimatization and dietary antioxidants. They evaluated the potential of acclimation to higher temperatures (20°C) and the ability of dietary antioxidants to mitigate the adverse effects of heat shocks (30°C) in rainbow trout (Oncorhynchus mykiss).

The Challenge: Rising Temperatures

Our water resources are changing, with rising temperatures, fluctuating salinity, and altered oxygen levels. These changes disrupt the delicate balance of aquaculture and lead to:

Rainbow trout thrive in cold water, typically between 10 and 15°C. However, water temperatures are exceeding these ideal ranges, causing significant problems for trout populations.

Fostering Resilience: Two Promising Strategies

This study investigated two methods to help rainbow trout cope with rising water temperatures:

  • Thermal Acclimatization: Gradually exposing juvenile rainbow trout to slightly warmer water (20°C) over a period before a major heat wave (30°C). This helps “train” the fish to adapt to a warmer environment.
  • Dietary Antioxidants: The trout were fed with food enriched with selenium (5 mg/kg) and polyphenols (2 g/kg), known for their antioxidant properties, which can help combat the harmful effects of heat stress.
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The Results: More Resilient Trout

The study found that the combination of these strategies offered the most significant benefits:

  • Improved Survival Rate: Exposing the trout to slightly warmer water (20°C) for 60 days before a heat shock improved their ability to withstand even higher temperatures (30°C) compared to trout acclimated to colder water (14°C). This suggests that acclimatization can trigger natural protective mechanisms in trout.
  • Stronger Immune System: Acclimatization and antioxidants stimulated the trout’s immune response, measured by increased immune cell activity and higher expression of immune-related genes.
  • Enhanced Antioxidant Capacity: These strategies also improved the trout’s natural antioxidant defenses, helping them counteract the harmful effects of heat stress.
  • Reduced Stress Response: Trout acclimated to warmer water, especially those fed with antioxidants, showed lower levels of stress hormones during heat exposure.

Application in Rainbow Trout Aquaculture

By implementing these strategies, aquaculture businesses can potentially help their rainbow trout populations adapt to a changing climate. Acclimatization and dietary adjustments offer a sustainable and practical solution to protect trout health and ensure the industry’s future.

Conclusion: A Better Future for Trout?

“The results of this study indicated that acclimatization to higher temperatures and/or feeding with diets supplemented with selenium and polyphenols can help mitigate the adverse effects of thermal shock in rainbow trout,” the researchers concluded.

These findings suggest that acclimatization to warmer waters and dietary antioxidants can significantly improve the rainbow trout’s ability to cope with heat stress. This research provides valuable insights for fish farmers and conservationists seeking to protect trout populations in a changing climate. By implementing these strategies, we can help ensure the future of these iconic cold-water fish.

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Moreover, the study paves the way for future research on optimizing these strategies. Future studies can explore:

  • Different acclimatization protocols.
  • Adjusting antioxidant levels in the diet for specific trout species and farming conditions.

The study was funded by the Shiraz University Council of Research.

Arya Vazirzadeh
Department of Natural Resources and Environmental Engineering, School of Agriculture, Shiraz University
Shiraz, Iran
Email: aryavazirzadeh@yahoo.com

Reference (open access)
Hosseinpour, F., Vazirzadeh, A., Farhadi, A., & Sajjadi, S. H. (2024). Acclimation to higher temperature and antioxidant supplemented diets improved rainbow trout (Oncorhynchus mykiss) resilience to heatwaves. Scientific Reports, 14(1), 1-14. https://doi.org/10.1038/s41598-024-62130-y