Salmonid farming has become a major global aquaculture industry. This involves first a freshwater phase where juvenile parrs develop to the pre-smolt stage, followed by smoltification–a key process enabling seawater adaptation. However, intensive farming negatively impacts growth and welfare, especially during highly stressful events such as smoltification. The stress response is primarily modulated by cortisol and has been described that acts binding both glucocorticoid (GR) and mineralocorticoid (MR) receptors. This is because fish do not synthesize aldosterone–the canonical MR ligand–but MR does. Nevertheless, recent findings suggest that 11-deoxycorticosterone (DOC) could play a role as a MR ligand (and might also by GR) generating different physiological effects. Although few previous studies described DOC actions during early salmonid stages, it is still unclear what role plays during the freshwater final phase, a critical step for proper smoltification. Hence, we aim to analyze the early DOC-induced response in rainbow trout (Oncorhynchus mykiss) pre-smolt juveniles by physiological and transcriptomic approaches using both GR and MR pharmacological antagonists. Thirty-six pre-smolts (~120 g and ~20 cm; n = 6 per each group) were two weeks acclimatized, later sedated and intraperitoneally injected with an endogenous cortisol inhibitor (1 mg/Kg metyrapone) plus antagonists for GR (1 mg/Kg mifepristone) or MR (1 mg/Kg eplerenone) for 1h, and then with DOC (1 mg/Kg) or vehicle as control (0.1% DMSO-PBS 1X) for 3h. After, plasma cortisol and DOC levels were measured, and the stress response was characterized at physiological and transcriptomic levels related to liver carbohydrate metabolism and gill osmoregulation. Increasing plasma-level in DOC, and decreasing calcium, phosphate, glucose, and pyruvate were detected. Only MR transcripts were downregulated by DOC. Additionally, liver glycogen levels increased by DOC and reversed by both antagonists, meanwhile muscle moisture decreased only with MR inhibitor. The qPCR in liver detected a differential expression of glucose/glycogen metabolism-related genes induced by DOC mainly via MR. Regarding gill RNA-seq, data revealed differentially expressed transcripts induced by DOC through GR and MR pathways. The enriched biological processes were mostly associated with ion transmembrane transport, stress response, carbohydrate metabolism, and innate immune response. Additionally, in vitro validation was made revealing differential gene expressions, low glucose uptake, no transepithelial resistance variations and decreasing apparent permeability, supporting the previous findings. In conclusion, data suggests that DOC has a significant role in trout pre-smolts’ stress response related to liver carbohydrate metabolism and gill osmoregulation through both receptors. This work could contribute to improving animal welfare monitoring during intensive culture conditions by featuring novel and potential molecular stress biomarkers during prior smoltification stages.
Funding: FONDECYT 1201498; FONDECYT 1230794; FONDAP 1522A0004; FONDAP 1523A0007; ANID-Subdireccioìn de Capital Humano Doctorado Nacional/2023/21230070; INI UNAB 2024.