This study explored the molecular mechanisms underlying egg quality deterioration due to in vivo postovulatory aging in pikeperch (Sander lucioperca L.), a key species in aquaculture. We employed tandem mass tag (TMT) peptide labeling coupled with LC–MS/MS quantitative proteomics to analyze eggs collected at various postovulation intervals. Our research revealed four distinct proteomic markers (Gins4, Atrx, DnaJB14, and Mrpl10) that are differentially expressed in response to early aging, shedding light on their potential roles in DNA replication, chromatin organization, protein folding, and mitochondrial function. The study confirmed that eggs maintain morphological integrity up to 5 h postovulation but exhibit compromised fertilization capacity, underscoring the importance of timely egg utilization in aquaculture practices. These findings enhance the understanding of egg aging at the molecular level, offering insights for improving reproductive success and larval quality in pikeperch aquaculture. The data are available via ProteomeXchange with the identifier PXD048349