Introduction
Cardiac responses to aquaculture conditions remain understudied in Atlantic bluefin tuna (ABFT, Thunnus thynnus). In other teleosts, such as Atlantic salmon, aquaculture-related stressors can induce morphological deviations and cardiac remodeling (Poppe et al., 2003; Gamperl & Farrell, 2004; Johansen et al., 2011; Frisk et al., 2020; Engdal et al., 2024; Vindas et al., 2024; Hvas et al., 2025). Here, we investigate whether farmed ABFT hearts exhibit morphological and histological differences compared to wild individuals and explore whether these are modulated by temperature.
Materials and Methods
We analyzed 209 hearts from wild and farmed ABFT (juveniles and adults) collected between 2020 and 2024. To evaluate thermal impacts, farmed juveniles were reared at two temperature regimes (mean ± sd 21.1 ± 4.3 °C, 24.2 ± 3.4 °C). Cardiac morphology was quantified using image analysis (Fiji/ImageJ), focusing on eight shape parameters. Histological sections (HES staining) were used to examine ventricular tissue composition.
Results
Preliminary results show distinct morphological differences between wild and farmed ABFT. Culture conditions are linked to ventricular remodeling in both adults and juveniles, while additionally altering bulbus alignment in adults and increasing ventricular elongation in juveniles. Relative ventricular mass (RVM) is consistently lower in farmed tuna across life stages. Juveniles cultured at higher temperatures exhibit ventricular remodeling and decreased bulbus arteriosus width. Furthermore, variations in ventricular elongation and RVM occur among wild juveniles captured in different geographic areas. Histological analysis reveals altered tissue composition in farmed individuals, more precisely a decreased relative compact myocardium area at both juvenile and adult stages. Final results will detail quantitative differences.
Discussion
This study presents the first quantitative assessment of the ABFT heart, demonstrating morphological and histological differences between farmed and wild ABFT that already emerge in juvenile stages. Linking cardiac responses to environmental conditions such as temperature may help explain how environmental variability influences cardiac performance in ABFT, providing a physiological basis for assessing resilience and adaptation in the wild.
Acknowledgment
This work was funded by EMFAF (European Maritime, Fisheries and Aquaculture Fund), NEWSPEC-MURCIA project.
References
Engdal, V. A., Dalum, A. S., Kryvi, H., Frisk, M., Torsvik, H., Hodne, K., Romstad, H., & Johansen, I. B. (2024). State of the heart: Anatomical annotation and assessment of morphological cardiac variation in Atlantic salmon (Salmo salar L.). Aquaculture, 578, 740046. https://doi.org/10.1016/j.aquaculture.2023.740046
Frisk, M., Høyland, M., Zhang, L., Vindas, M. A., Øverli, Ø., & Johansen, I. B. (2020). Intensive smolt production is associated with deviating cardiac morphology in Atlantic salmon (Salmo salar L.). Aquaculture, 529, 735615. https://doi.org/10.1016/j.aquaculture.2020.735615
Gamperl, A. K., & Farrell, A. P. (2004). Cardiac plasticity in fishes: Environmental influences and intraspecific differences. Journal of Experimental Biology, 207(15), 2539–2550. https://doi.org/10.1242/jeb.01057
Hvas, M., Folkedal, O., Vindas, M. A., & Johansen, I. B. (2025). Physiological performance and cardiac morphology of Atlantic salmon reared under slow and fast growth conditions. Aquaculture Reports, 42, 102730. https://doi.org/10.1016/j.aqrep.2025.102730
Johansen, I. B., Lunde, I. G., Røsjø, H., Christensen, G., Nilsson, G. E., Bakken, M., & Øverli, Ø. (2011). Cortisol response to stress is associated with myocardial remodeling in salmonid fishes. Journal of Experimental Biology, 214(8), 1313–1321. https://doi.org/10.1242/jeb.053058
Poppe, T. T., Johansen, R., Gunnes, G., & Tørud, B. (2003). Heart morphology in wild and farmed Atlantic salmon Salmo salar and rainbow trout Oncorhynchus mykiss. Diseases of Aquatic Organisms, 57(1–2), 103–108. https://doi.org/10.3354/dao057103
Vindas, M. A., Engdal, V. A., Kavaliauskiene, S., Folkedal, O., Höglund, E., Moyano, M., Øverli, Ø., Frisk, M., & Johansen, I. B. (2024). Importance of environmental signals for cardiac morphological development in Atlantic salmon. Journal of Experimental Biology, 227(20), jeb247557. https://doi.org/10.1242/jeb.247557