Introduction
Egg quality is a key determinant of reproductive success in Atlantic salmon (Salmo salar), yet the biochemical basis underlying its variation remains poorly understood. Variability in egg quality can significantly affect fertilisation success, embryo survival, hatching rate, and embryo viability, ultimately impacting production efficiencies (Bobe & Labbe, 2010; Brooks et al., 1997). In the past, egg quality in salmonids has been evaluated using post fertilisation outcomes which do not provide insight into the underlying biochemical processes that determine egg developmental competence (Aegerter & Jalabert, 2004; Lahnsteiner, 2000). Metabolomics has been applied to study fish responses to stress, nutrition, and disease, but its use in assessing egg quality remains limited. To the best of our knowledge, this is the first study to characterise the pre‑fertilisation metabolomic profile of Atlantic salmon eggs, aiming to identify metabolites that distinguish egg batches by fertilisation success using a commercial Tasmanian population.
Materials and Methods
Freshly spawned unfertilised eggs were obtained from fifteen three-year-old Atlantic salmon females, and highly motile sperm was collected from two three-year-old neo-males at a Tasmanian hatchery in May 2024. Prior to fertilisation, subsamples were collected for metabolomic analysis. Each egg batch was fertilised in duplicate using sperm from both males and incubated individually in custom-made mini upwellers within a temperature and dissolved oxygen controlled freshwater recirculation system. Fertilisation success was assessed after three weeks of incubation based on neural streak formation. Eggs were subsequently freeze-dried, and metabolites were extracted using acetonitrile/methanol/water (2:2:1, v/v/v). Metabolite separation was performed using ultra-high-performance liquid chromatography (UHPLC), and annotation was conducted using a preliminary version of the Metabolite Annotation Propagation Synthesis (MAPS) pipeline (Cowled et al., 2026). Metabolic differences between high- and low-quality egg batches (defined by fertilisation success rate) were characterised using MetaboAnalyst 6.0 (Pang et al., 2024) to identify pathways associated with developmental competence.
Results and Discussion
A total of 1209 features were detected across egg samples, with 303 metabolites annotated in positive ion mode and 109 in negative ion mode. Low-quality eggs exhibited significantly higher levels of cyclic adenosine monophosphate (cAMP), spermine, D-camphor, and pivaloyltaurine. Pathway enrichment analysis reflected localised perturbations in amino acid metabolism and redox balance. These findings suggest the presence of metabolic stress, disrupted redox homeostasis, and changes in polyamine metabolism that may impair oocyte maturation and early embryonic development. High-quality eggs were characterised by increased levels of peptides and lipid-associated metabolites such as leucyl-prolyl-glycine, alanyl-valyl-proline isobutylamide, asparaginylleucine, glycyl-L-leucine, rhodinyl acetate, diphenyl sulfone, and clopidogrel. The enrichment of dipeptides and tripeptides may indicate enhanced amino acid availability for protein synthesis, while lipid-related metabolites suggest improved energy reserves and nutritional status.
Our study demonstrates distinct metabolic signatures associated with egg quality and fertilisation success in Atlantic salmon and propose potential biochemical markers for improving broodstock management and reproductive performance in Atlantic salmon aquaculture.
Acknowledgement
This work was funded by Huon Aquaculture Group, Tassal Group Limited and Biomar Group A/S conducted under Dr Harry King Memorial PhD Scholarship.
References
Aegerter, S., & Jalabert, B. (2004). Effects of post-ovulatory oocyte ageing and temperature on egg quality and on the occurrence of triploid fry in rainbow trout, Oncorhynchus mykiss. Aquaculture, 231(1-4), 59-71. https://doi.org/10.1016/j.aquaculture.2003.08.019
Bobe, J., & Labbe, C. (2010). Egg and sperm quality in fish. General and Comparative Endocrinology, 165(3), 535-548. https://doi.org/10.1016/j.ygcen.2009.02.011
Brooks, S., Tyler, C. R., & Sumpter, J. P. (1997). Egg quality in fish: what makes a good egg? Reviews in Fish Biology and Fisheries, 7(4), 387-416. https://doi.org/10.1023/a:1018400130692
Cowled, M. S., Liu, S., Wang, X., Soerianto, T., Harris, B. A., Reddy, P., De Souza, D. P., & McConville, M. J. (2026). Mapping out the Metabolome: Metabolite Annotation Propagation and Synthesis (MAPS). ChemRxiv(0220). https://doi.org/10.26434/chemrxiv.15000268/v1
Lahnsteiner, F. (2000). Morphological, physiological and biochemical parameters characterizing the over-ripening of rainbow trout eggs. Fish Physiology and Biochemistry, 23(2), 107-118. https://doi.org/10.1023/a:1007839023540
Pang, Z., Lu, Y., Zhou, G., Hui, F., Xu, L., Viau, C., Spigelman, Aliya F., MacDonald, Patrick E., Wishart, David S., Li, S., & Xia, J. (2024). MetaboAnalyst 6.0: towards a unified platform for metabolomics data processing, analysis and interpretation. Nucleic Acids Research, 52(W1), W398-W406. https://doi.org/10.1093/nar/gkae253