044 | Thyroid response to stress in illness Caretta caretta: a preliminary study

The loggerhead sea turtle (Caretta caretta) is classified as endangered on the IUCN Red List and is threatened by both infectious diseases and anthropogenic activities [1]. Consequently, many individuals are admitted in rescue centers for long-term rehabilitation. Hormone levels are reliable indicators of individual and population health, as well as of environmental impact and stress [2]. Corticosterone (CORT) is the primary glucocorticoid hormone produced by sea turtles in response to stressors [1]. Thyroid hormones also respond to stress and are studied as a complement to corticosterone. These are essential for normal development and physiological functions in vertebrates and, in sea turtles, regulate energy-demanding processes such as growth, metabolism, development, and reproduction [2]. The aim of this study was to evaluate stress response in C. caretta, by the CORT and thyroid hormones (T3, T4 and TSH) assessment. Twenty-six loggerhead sea turtles hospitalized at the C.Re.Ta.M. rescue center were included in the study. On each animal, curved carapace length (CCL) and body weight were recorded, and on the basis of that, divided into two groups: juveniles (n.13; CCL 32±6.2 cm) and sub-adults (n.13; CCL 51.7±11 cm). Blood samples were collected from the dorsal cervical sinus using lithium-heparin tubes. Plasma concentrations of CORT, T3, T4 and TSH were measured by enzyme-linked immunosorbent assay (ELISA) using commercial kits (Assay Genie). Statistical analyses were performed using GraphPad Prism 5. Data were not normally distributed. Spearman’s correlation analysis revealed no significant associations among the measured hormones. Hormonal concentrations between juveniles and sub-adults were compared using the Mann–Whitney U test, which showed significantly higher CORT levels in juveniles compared to sub-adults (p=0.023). Overall, turtles hospitalized at C.Re.Ta.M. exhibited higher CORT levels compared to those reported in previous studies [1,2,4], likely due to stressors such as fin injuries, ingestion of hooks, fishing lines, or plastic debris. Although chronic stress is known to alter endocrine regulation and potentially suppress thyroid axis activity [5], our results showed no differences in the thyroid hormones concentration between the two group, contrary to that observed in previous studies [3,4]. Despite elevated stress levels, thyroid hormones did not show a predictable pattern in these sea turtles. Variations in thyroid hormone concentrations may be influenced by metabolic condition, environmental temperature, and life-history stage [2,3,4]. Given the limited number of studies on the endocrine profile of C. caretta, further studies are needed to better understand stress responses and the factors driving hormonal variability in this species.