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Resumo(s)
We investigated the physiological, endocrine, and histological responses of juvenile stellate sturgeon (Acipenser stellatus) to salinity challenge across four weight classes (0.89 ± 0.21, 2.01 ± 0.32, 4.84 ± 0.39, and 9.07 ± 1.47 g; mean ± S.E.) and four salinity levels (0, 4, 8, and 12 ppt) over acute to chronic exposure (3–624 h). A total of 4800 juveniles were used across four sequential experiments, with 100 ± 5 fish per tank (12 tanks per experiment). A replicated factorial design (three tanks per treatment) enabled robust assessment of ionoregulation, stress response, and tissue integrity. Plasma osmolality increased from approximately 230 to 266 mOsm kg− 1 during early exposure, followed by progressive convergence toward a narrower physiological range (≈251–284 mOsm kg− 1 ) at 624 h, indicating partial osmotic compensation. This adjustment was driven primarily by sodium, which exhibited the strongest salinity- and size-dependent response, confirming its central role in extracellular osmotic regulation. In contrast, potassium displayed pronounced size-dependent dysregulation, with markedly elevated concentrations in fish 3 g maintained values within or near the physiological range. Cortisol dynamics revealed a clear ontogenetic shift in stress responsiveness. Smaller juveniles (3 g) demonstrated more efficient recovery, with the 5–10 g group achieving ~92% recovery by 96 h, compared to only ~45% in the smallest size class. These endocrine patterns were consistent with ionoregulatory performance and further support a size-dependent transition in physiological resilience. Histopathological analysis corroborated systemic findings. Histopathological analysis using a semi-quantitative scoring system (0–4) revealed significant size- and salinity-dependent tissue alterations. Gill tissues showed lamellar fusion, epithelial lifting, hyperplasia, necrosis, and hemorrhage, with more severe lesions in smaller juveniles at intermediate to high salinities. Kidney tissues exhibited glomerular expansion, tubular degeneration and obstruction, congestion, hemorrhage, and hemosiderin deposition, with lesion severity generally decreasing with increasing body size. These histological patterns were consistent with physiological and endocrine responses and reflected greater structural resilience in larger juveniles under salinity stress. Collectively, these integrated responses identify an empirical transition zone at approximately 3 g under the tested conditions, below which juveniles exhibit limited capacity to maintain physiological homeostasis under salinity challenge. Above this threshold, fish display more effective physiological regulation, resulting in better ion balance, lower stress, and improved tissue integrity. Together, these findings provide mechanistic evidence for size-based acclimation protocols, gradual salinity transitions, and optimized release strategies to enhance survival and performance in aquaculture and stock enhancement programs.
Descrição
Palavras-chave
Acipenser stellatus Salinity tolerance Ion regulation Plasma osmolality Histopathology
Contexto Educativo
Citação
Editora
Elsevier