Salmonid aquaculture is one of the most significant sectors within global fish farming, playing a key role in meeting the growing demand for aquatic food. While Atlantic salmon dominates international markets, the farming of rainbow trout (O. mykiss ) represents a vital component of the industry, particularly in freshwater systems. Rainbow trout is widely appreciated for its adaptability, fast growth rate, and high nutritional value, and is cultivated across a variety of production scales and environmental conditions. However, intensive aquaculture practices frequently expose fish to multiple stressors. These stressors can compromise immune function, hinder growth, and adversely affect overall fish health and welfare, posing a significant challenge to the long-term sustainability of aquaculture systems. Cortisol, the primary glucocorticoid in teleost fish, is essential for maintaining homeostasis during stress by regulating key physiological functions such as metabolism, osmoregulation, immune activity, and energy balance. It exerts its effects through binding to intracellular glucocorticoid receptors (GRs), which in turn modulate the transcription of target genes via glucocorticoid response elements (GREs). Although the metabolic roles of cortisol are well established, its prolonged effects on gene expression in skeletal muscle in rainbow trout remain insufficiently characterized. Given that skeletal muscle is the largest tissue in fish and plays a central role in growth and metabolic regulation, it serves as a suitable model for investigating molecular responses to sustained cortisol exposure. Previous research has shown that early-life exposure to cortisol can alter the transcriptomic profile of muscle tissue, influencing pathways related to energy metabolism, stress signaling, and proteolysis/autophagy. However, it remains uncertain whether such transcriptomic alterations are maintained or evolve under prolonged hormonal stimulation. In the present study, using RNA-Seq, the global modulation of gene expression in the skeletal muscle of rainbow trout was analyzed two weeks after exogenous administration of cortisol, using coconut oil as a vehicle, compared to a control group. Total RNA was extracted from skeletal muscle samples, and cDNA libraries were constructed and sequenced using the Illumina NovaSeqX platform (150 bp PE). Differential expression and gene ontology enrichment analyses were performed to identify biological processes and pathways regulated by cortisol. The analysis included the validation of candidate genes by RT-qPCR. Differentially expressed genes and pathways related to physiological processes relevant to stress adaptation in juvenile rainbow trout were identified. These results will contribute to understanding molecular mechanisms associated with chronic stress in fish, providing tools to optimize stress management and muscle development in aquaculture.
Funding: FONDECYT 1230794; FONDAP 1522A0004; FONDAP 1523A0007;