Shellfish aquaculture plays a crucial role in sustainable aquaculture production, with the Eastern oyster, Crassostrea virginica, being one of the most important species in the United States. However, the expansion of the oyster aquaculture industry in the Gulf of Mexico (GoM) is restricted by a limited supply of seed and incidences of high mortality in hatcheries. The high demand for quality seed with enhanced growth and survival necessitates improvement in the consistency of larval production to increase commercial hatchery production for the GoM. Ongoing production issues are caused by several factors, with low gamete quality being a significant contributor.
This study aimed to identify biomarkers for egg quality to improve the efficiency of Eastern oyster hatcheries. Five cohorts of diploid oysters were spawned from July through September 2023 using natural spawning methods. Eggs were collected from nine females during each spawn, and a subset was digitally imaged for morphometrics. An additional subset was flash-frozen for fatty acid analysis. The remaining eggs were separated into three groups, each fertilized with a different male. All fertilized eggs from a given female were then pooled, fertilization rates were determined, and eggs were separated into three replicate 800 mL beakers to assess survival. At 24 hours post-fertilization, larvae that had reached the D-hinge stage were counted and measured. Females with the highest and lowest survival rates were selected and categorized as “good” or “bad,” corresponding to >81% and <62% survival, respectively, and egg biomarkers were compared. Egg morphometrics were not significantly different between good and bad eggs. However, fatty acid profiles were different, with good-quality spawns having higher abundances of saturated fatty acids. Docosahexaenoic acid (DHA) levels were correlated with season, with the gametes from the September spawns having higher DHA levels than those from the July spawns.
These findings identify egg quality biomarkers that correlate with 24-hour survival. Future studies will compare gene expression profiles between high- and low-quality eggs to determine molecular mechanisms for game quality. These results will allow hatcheries to prioritize fertilization of high-quality gametes and develop broodstock conditioning protocols that improve gamete quality, enhancing hatchery production and providing a more consistent supply of larvae by minimizing the losses commonly associated with larval rearing.