IntroductionFish welfare assessment has become a central concern in marine aquaculture, both for optimising production efficiency and addressing growing consumer awareness. Gilthead seabream (Sparus aurata), one of the most commercially significant species in Mediterranean aquaculture, is farmed under a range of systems including conventional and organic regimes, yet science-based welfare evaluation tools grounded in real farming data remain scarce. This study aimed to assess S. aurata welfare across contrasting aquaculture environments by combining established physiological indicators with cutting-edge biotelemetric monitoring at two operational sea farms.
Materials and Methods
The investigation was carried out at two offshore cage farms in Sardinia, Italy: a conventional facility A and a certified organic operation B, over an approximately four-month period (August–November 2024). A multidisciplinary framework integrated classical welfare indicators, including growth performance and a suite of stress, immune, and metabolic blood markers (haematological parameters, lactate, glucose, cortisol, IGF-1, total protein), with surgically implanted biotelemetric tags. These tags, incorporating accelerometers and depth sensors, recorded continuous swimming activity and vertical habitat use in a subset of fish over roughly 100 days. Data were analysed through both univariate and multivariate statistical methods.
Results
Substantial inter-site and temporal differences emerged across parameters. Multivariate analysis indicated superior welfare status in fish from Stintino, evidenced by greater growth performance and elevated total protein levels, suggestive of a stronger immunological condition. Despite higher circulating lactate, fish from the B site displayed lower acceleration values, pointing to a reduced reliance on anaerobic pathways relative to fish at A site. Fish from the conventional site appeared more metabolically constrained, potentially limiting their resilience to future stressors. Growth disparities between sites were attributed primarily to age-related differences rather than differential metabolic allocation. Multiple site-specific factors, including environmental conditions, stocking density, feed regimes, and predator interactions near the cages, likely underlie the observed metabolic divergence. Telemetry further revealed clear diel activity patterns and marked inter-site differences in vertical distribution, driven by environmental cues and potential predator presence. Acceleration profiles were also consistent with feeding-anticipatory behaviour, corroborating existing literature.
Conclusion
This study delivers a detailed characterisation of growth, health, and welfare indicators under operational farming conditions, highlighting the complexity inherent in welfare interpretation when multiple parameters yield divergent signals. The multi-indicator framework employed here provides a robust and comprehensive welfare assessment alongside a unique real-world dataset for S. aurata reared in open-sea cages. These findings constitute a meaningful baseline for future research aimed at explaining the inter-individual, inter-site, and temporal variability observed in farmed gilthead seabream.
AcknowledgmentThis research was funded by the Italian Ministry of Health (Project IZS SA 07/2021 RC). Authorization of the experimental procedure was n.522/2023PR.