Aquaculture has traditionally been practiced in sheltered areas such as inland ponds or coastal bays, and the expansion of open marine environments for fish farming presents a compelling solution.
Open-ocean aquaculture offers several advantages, including the potential to reduce waste accumulation, exposure to parasites, and algal blooms compared to traditional aquaculture methods, which have a significant impact on fish health and welfare.
However, the effects of open-ocean fish farming on the health and welfare of fish remain largely speculative, and the complex interaction of environmental variables and management practices on fish mortality and parasite loads has not been thoroughly explored.
Researchers from The Scottish Association for Marine Science (SAMS), the University of Stirling, Mediterranean Institute for Advanced Studies (IMEDEA-CSIC/UIB), Xelect Ltd., Mowi Scotland Ltd., and the University of Exeter published a study aimed at assessing the impact of wave exposure, in combination with other factors, on the health and welfare of Atlantic salmon (Salmo salar) in open-sea net pens in Scotland. The results shed light on the potential challenges and benefits of expanding aquaculture into more energetic marine environments.
Over a 20-month period, researchers collected data from eight Atlantic salmon farming sites in Scotland, situated along a wave exposure gradient. They collected information on salmon health, mortality, the use of anti-parasitic treatments, and more.
This extensive dataset allowed researchers to evaluate the influence of wave exposure on fish health and welfare and how it interacts with other variables.
Key Study Findings
“Prolonged wave exposure had a minimal direct effect on farmed salmon mortality rates or sea lice infestations. The primary effect of wave exposure occurred through interactions with other stressors,” reported the scientists.
The study’s results suggest that “higher wave exposure may act as a chronic stress factor, contributing to allostatic load accumulation in farmed Atlantic salmon.”
Mortality Rate and Wave Exposure
One of the study’s key findings was that wave exposure significantly modulated the effects of other variables on fish mortality. Farms with higher wave exposure experienced more pronounced increases in mortality rates over time and in response to extreme temperatures. This suggests that offshore farms in more energetic environments may face greater challenges in maintaining fish health and welfare, especially during periods of environmental stress.
Parasite Infections and Wave Exposure
The study also revealed a correlation between wave exposure and the prevalence of sea lice infections in Atlantic salmon. “The interactive effects of wave exposure with acute stressors were similar concerning lice infestations,” the researchers reported.
Sea lice infections tended to increase over time, and farms with higher wave exposure experienced more pronounced increases, particularly with higher scores of amoebic gill disease (AGD) and high temperatures.
Additionally, the impact of AGD on fish health was more pronounced in low-velocity waters, highlighting the intricate relationship between various factors.
Management Practices and Uncertainty
Interestingly, the study found that anti-parasitic treatments were more frequently applied in farms with low wave exposure. This observation introduced an element of uncertainty regarding the impact of these treatments on fish welfare in different farms.
The interactions between wave exposure and management practices are complex and underscore the need for a nuanced approach to aquaculture in marine environments.
Implications for Marine Aquaculture
The study’s results emphasize the importance of considering the cumulative impact of multiple stressors on fish health and welfare in marine aquaculture. It suggests that expanding aquaculture into more energetic marine environments may have negative consequences in certain circumstances, necessitating adaptation of practices.
The more pronounced increase in fish mortality over time in high-wave exposure environments could have implications for the duration of fish production cycles, raising questions about the sustainability of coastal aquaculture under such conditions.
Furthermore, the dramatic impacts of warm temperatures on fish health in farms exposed to high waves demand careful consideration of water temperature changes, both coastal and marine.
In conclusion, this scientific analysis provides valuable insights into the complex relationship between wave exposure and other environmental variables on fish health and welfare in marine aquaculture. The study underscores the need for ongoing research and the development of innovative practices to ensure the sustainable growth of this critical sector while safeguarding fish welfare and the quality of seafood production.
The study was funded by the UKRI BBSRC/NERC project Off-Aqua (Evaluating the Environmental Conditions Required for the Development of Offshore Aquaculture).
Tim M. Szewczyk
The Scottish Association for Marine Science, SAMS
Dunbeg, Oban, Argyll PA37 1QA, UK.
Reference (open access)
Tim M. Szewczyk, Bernat Morro, Carlos Díaz-Gil, Philip A. Gillibrand, Jon P. Hardwick, Keith Davidson, Dmitry Aleynik, Sònia Rey Planellas. 2023. Interactive effects of multiple stressors with significant wave height exposure on farmed Atlantic salmon (Salmo salar) welfare along an inshore-offshore gradient, Aquaculture,
Volume 579, 2024, 740184, ISSN 0044-8486, https://doi.org/10.1016/j.aquaculture.2023.740184.