Introduction
Manipulating spawning time doesn’t just extend the breeding calendar - it initiates molecular responses that can shape the next generation . In aquaculture, altering environmental cues such as temperature and photoperiod to shift the spawning window is a well-established strategy to ensure year-round offspring production . While effective in practice, the broader biological consequences of this approach across generations remain insufficiently understood . Delaying spawning in Atlantic salmon reduced egg quality but had no effect on fecundity and improved fry size (Fjelldal et al. 2024) . Manipulating spawning time also altered egg nutrient profiles, which may suggest potential impacts on offspring through metabolic programming (Skjærven et al. 2020 ; Skjærven et al. 2022 ). Saito et al. (2025) linked a manipulation of spawning time to altered DNA methylation profiles in salmon fry livers with potential implications for growth and development , however, little is known about how such reproductive interventions impact muscle growth. This study explores how extending the spawning season of Atlantic salmon - comparing delayed vs. normal spawning - impacts the nutritional, transcriptomic and epigenetic programming of both muscle and liver in first-feeding fry.
Material and methods
Unfertilized eggs and first-feeding fry (~845 degree-days ) derived from broodstock exposed to either normal or delayed spawning conditions were sampled. We analys ed free and protein-bound amino acid profiles in unfertilized eggs and first-feeding fry to assess nutrient status and early metabolic regulation. RNA was extracted from muscle and liver of first-feeding fry for RNA-sequencing and genomic DNA for EM-sequencing to assess gene expression and methylation landscapes.
Results
Preliminary results revealed a stronger transcriptional response in muscle than in liver of first-feeding fry, with a n approximately fivefold increase in differentially expressed genes between the spawning groups, indicating a more pronounced tissue-specific response in muscle at this early developmental stage. In parallel, amino acid profiling of both eggs and fry showed distinct metabolic signatures between the spawning seasons, which are suggestive of compensatory adjustments in response to the nutrients supplied by the mother to the yolk . These metabolic shifts showed alignment with the gene expression changes. Across both tissues, differentially expressed genes were enriched in pathways related to energy metabolism, protein turnover, and one-carbon (1C) metabolism - key processes known to influence the methylation potential. Ongoing epigenetic analyses will provide insight into regulatory pathways affected by these molecular changes at early life stages .
Discussion and Conclusion
These findings indicate that extending the spawning season modulates offspring development at both metabolic and molecular levels . Notably, delayed spawning resulted in larger fry, suggesting enhanced early growth potential despite reduced egg quality. This growth advantage may be linked to the transcriptional changes observed in muscle tissue, which appears particularly responsive to altered spawning conditions . By combining gene expression, amino acid profiles, and epigenetic data , this study provides a foundation for understanding how altered spawning timing shapes offspring physiology at multiple biological levels. This knowledge may support the refinement of spawning strategies and nutritional protocols to optimize robustness performance in commercial aquaculture.
References
Fjelldal et al., 2024. Spawning manipulation, broodfish diet feeding and egg production in farmed Atlantic salmon. Aquaculture. https://doi.org/10.1016/j.aquaculture.2023.740227
Skjærven et al., 2020. Out-of-season spawning affects the nutritional status and gene expression in both Atlantic salmon female broodstock and their offspring. Comp Biochem Physiol A. https://doi.org/10.1016/j.cbpa.2020.110717
Skjærven et al., 2022 . Earlier or delayed seasonal broodstock spawning changes nutritional status and metabolic programming of growth for next-generation Atlantic salmon . Aquaculture. https://doi.org/10.1016/j.aquaculture.2022.738187
Saito et al., 2025. Altered spawning seasons of Atlantic salmon broodstock genetically and epigenetically influence cell cycle and lipid-mediated regulations in their offspring. PLoS ONE. https://doi.org/10.1101/2024.02.03.578741