Identification of sex and reproductive protein biomarkers in conditioned water of the Sydney rock oyster

The Sydney rock oyster (SRO), Saccostrea glomerata, is one of the most important aquaculture species in Australian, and improving production techniques is essential for creating reliable, sustainable farming practices with increased profitability. Broodstock sex identification is a significant challenge since they do not display any external sexual dimorphism and current sex identification approaches rely on invasive and destructive techniques that compromise broodstock integrity. Therefore, this study investigated whether SROs secrete sex and reproductive stage-specific semiochemical protein profiles that could be used for sex identification. Following proteomic analysis of oyster-conditioned water at two different reproductive stages (ripe and spent) for each sex, we demonstrate that SROs do secrete a distinct sex and reproductive stage protein profile. Functional annotation revealed these secreted proteins are potentially involved in metabolic processes, immunity and chemical communication. Furthermore, semi-quantitative analysis facilitated identification of candidate female-specific protein biomarkers, with primary targets for further investigation being temptin and byssal protein-3-like proteins. Both proteins showed high gene expression in the oyster's digestive gland and were abundant in the conditioned water of females. In conclusion, this study has established that SROs release distinctive protein profiles, some of which may be utilized as biomarkers to infer sex and reproductive stage non-invasively. This foundational knowledge provides a basis for developing novel approaches for non-invasive detection of oyster sex, reproductive stage, and immune status, thereby offering significant benefits to aquaculture industry operations.