A recently published study in Scientific Reports reveals that environmental enrichment (EE) during the early life stages of Atlantic salmon (Salmo salar) has long-lasting positive effects on their well-being. This finding is not only crucial for the salmon industry but also for scientific research that uses fish as model organisms.
The research, conducted by a team of scientists from the Animal and Veterinary Science Research Group (SRUC), the Institute of Aquaculture at the University of Stirling, the Universidade de Vigo, and the University of South Bohemia in České Budějovice, highlights the importance of providing enriched environments to promote positive emotional states, reduce stress, and enhance cognitive abilities in captive fish.
The importance of fish welfare in aquaculture
Contrary to past beliefs, fish are sentient beings. They can feel pain, possess complex cognitive abilities, engage in social interactions, and experience both positive and negative emotions. Therefore, ensuring their well-being is an ethical and legal responsibility.
Moreover, fish welfare directly influences the quality of scientific research. A stressed or unhealthy fish can alter study results, compromising their validity and reproducibility.
The study emphasizes the need for a holistic approach to assessing fish welfare, considering factors such as physical integrity, physiology, behavior, and mental well-being. Traditional welfare interventions have focused on minimizing negative states such as pain, hunger, and stress.
However, promoting positive welfare states—such as exploration, foraging, and social interactions—has received less attention. Positive Animal Welfare (PAW) goes beyond merely preventing suffering; it aims to provide animals with rewarding experiences that allow them to thrive in captivity.
Environmental enrichment: A path to positive welfare
Environmental enrichment involves adding structures or stimuli to the rearing environment that encourage natural behaviors and mental engagement. For juvenile Atlantic salmon, this could include shelters, novel substrates, or variations in water flow.
The study assessed whether providing such enrichment during early life stages could improve welfare indicators, including morphological traits (fin damage, body condition), physiological responses (plasma cortisol levels), and behavioral traits (activity, group cohesion, and neophobia).
Researchers reared Atlantic salmon fry in enriched and non-enriched tanks for 13 weeks. The enriched tanks contained suspended artificial plants, whereas the non-enriched tanks were empty. The team measured various welfare indicators throughout the experiment and found that environmental enrichment had several positive effects on the fish.
Key findings: Behavioral and physiological benefits
Behavioral improvements
Fish raised in enriched environments exhibited more cohesive group behavior and were less neophobic (fearful of novelty) compared to those in non-enriched tanks. Enriched fish also recovered more quickly from exposure to a novel object, suggesting lower anxiety levels and better stress-coping mechanisms.
Cognitive and neurogenic enhancements
The study found that enriched fish had increased expression of genes related to neural development and activity (bdnf and ndf1), as well as a higher serotonergic turnover. These changes indicate improved cognitive function and neuroplasticity, which are crucial for learning, memory, and stress response.
No negative impact on growth or health
Importantly, the provision of environmental enrichment did not negatively affect growth, fin damage, or body condition. This suggests that enriched environments can enhance welfare without compromising the physical health of the fish.
Implications for aquaculture and research
The findings have significant implications for aquaculture practices and fish welfare research. By providing enriched environments, aquaculturists and researchers can promote positive welfare states in captive fish, leading to healthier and less stressed populations. This, in turn, can improve the reliability and reproducibility of scientific studies conducted on these animals.
The study also highlights the importance of life-stage-specific enrichment. Juvenile salmon, for example, benefit from environments that mimic their natural habitats, fostering behaviors such as exploration and social interaction. Early-life experiences have lasting effects on behavior and physiology, and providing enrichment during these critical stages can lead to better outcomes in adulthood.
Conclusion
Environmental enrichment is an investment in fish welfare and scientific quality. By adopting environmental enrichment practices in aquaculture and research, a more sustainable and ethical future for the salmon industry can be ensured.
The research underscores the benefits of environmental enrichment in promoting positive welfare for juvenile Atlantic salmon. By enhancing emotional states, reducing stress, and improving cognitive abilities, enriched environments can help ensure that captive fish are not only free from negative experiences but also have access to positive ones.
Contact
Pamela M. Prentice
Animal Behaviour and Welfare, Animal and Veterinary Science Research Group, SRUC
West Mains Rd, Edinburgh, EH9 3JG, UK
Institute of Aquaculture, Faculty of Natural Sciences, University of Stirling
Stirling, UK
Email: pprentice@sruc.ac.uk
Sonia Rey Planellas
Animal Behaviour and Welfare, Animal and Veterinary Science Research Group, SRUC
West Mains Rd, Edinburgh, EH9 3JG, UK
Email: sonia.reyplanellas@stir.ac.uk
Reference (open access)
Prentice, P. M., Chivite Alcalde, M., Císař, P., & Rey Planellas, S. (2025). Early-life environmental enrichment promotes positive animal welfare for juvenile Atlantic salmon (Salmo salar) in aquaculture research. Scientific Reports, 15(1), 1-16. https://doi.org/10.1038/s41598-025-88780-0
