Shellfish hatcheries are essential in the shellfish farming process, and seed availability can limit the expansion of the shellfish aquaculture industry. Many hatcheries encounter challenges that hinder efforts to maximize seed production. This project represents a collaboration between an academic research team and a commercial shellfish hatchery in Virginia, USA to address an existing bottleneck of additional production of eastern oyster (Crassostrea virginica) seed. This hatchery capitalizes on optimal water quality for larval culturing, which is best during the winter and early spring. To take advantage of this high-quality water, the hatchery begins its spawning season in January and has developed a holding system to maintain seed for up to 8 weeks under cold conditions until seed can be moved to outside nursery systems when outside water temperatures exceed 10°C. Prior to moving outside, seed are typically warmed to 27°C. While early season production results in millions of extra seed, the current holding practice can produce losses of up to 50%, manifesting as stunted growth and mortality.
This project addressed whether the length of the cold holding duration (CHD) influences seed physiology and if an acclimation period during the warm-up to 27°C would improve performance. We hypothesized that the existing mortality and growth issues stem from physiological stress during extended CHD and a subsequent abrupt temperature increase. To investigate this, we raised eastern oyster seed at 15°C for three different CHD lengths (8 weeks: CHD8, 6 weeks: CHD6, and 4 weeks: CHD4). Each seed group was then divided and subjected to either a fast warming treatment (reaching 27°C in one day) or a slow warming treatment (gradually reaching 27°C by the end of the warming period) for 8-9 days. We measured oxygen consumption (as a proxy for metabolic rate, MO2), triglyceride (TG) and total protein (TP) reserves, total antioxidant capacity (TAC), and lipid peroxidation (LP) throughout both the CHD and warming periods.
Preliminary results suggest that shorter CHD durations and slow warming may create less stressful conditions for oyster seed. By the end of the CHD, all seed groups exhibited similar MO2. The CHD8 and CHD6 groups experienced a decrease in MO2 towards the end of the CHD, while the CHD4 group maintained consistent MO2 throughout. All groups showed an increase in TG and TP content over time and similar levels, respectively by the end of the CHD. Under fast warming, MO2 in all CHD groups peaked on the first day and then decreased significantly. Under slow warming, the CHD6 group followed a similar pattern to the fast warming group, while CHD4 and CHD8 showed no changes in MO2 over time. There was no significant effect of warming regime on TG and TP levels. However, TG content decreased significantly and TP levels increased significantly by the end of the warming period for most groups. TAC and lipid peroxidation results will be discussed. Overall, these findings highlight the potential for optimizing holding durations and warming protocols to enhance seed health and reduce mortality in oyster hatchery practices.