EFFECT OF COHORT ON PHYSIOLOGICAL PARAMETERS OF EASTERN OYSTERS Crassostrea virginica BRED AT SEPARATE HATCHERIES IN THE GULF OF MEXICO

 Louisiana  has a  long history of oyster farming, however, many farmers in the region are now experiencing high oyster mortality. These mortality events could be caused by environmental stressors such as low salinity or high water temperature, pathogen infection (Perkinsus marinus ), stress from gametogenesis, or other unexplained causes. To address these challenges the germplasm of oysters native  to Louisiana  could be stored in germplasm repositories . This would provide  oyster hatcheries easy access to a wide variety of genetics for breeding programs without the burden of having to maintain multiple  lines as live oysters . Germplasm from oysters bred at hatcheries could also be stored allowing for easy reconstitution of lines .  However,  the hatchery that breeds a particular oyster line could be an important factor when trying to predict performance in the field. During a 2019-2020 field study, mortality differences were observed among the same lines of oysters (the progeny of  Calcasieu Lake, Vermillion Bay, and  Sister Lake  wild broodstock) bred at two different hatcheries. The two hatcheries were the Auburn University Shellfish Lab (AUSL) and the Louisiana Sea Grant Oyster Research Lab (LSU), and oysters bred at each hatchery constituted the two cohorts of the study.

 To investigate  potential differences  between cohorts, diploid and triploid Sister Lake oysters from both cohorts were transported to the Animal & Food Sciences Department at LSU. There, the maximum oxygen consumption rates (VO2 max), absorption efficiencies, ammonia excretion rates, clearance rates, P. marinus infection intensities, and mortality rates of oysters were measured. Oysters from the AUSL cohort had  higher VO2 max after withholding food for 7 days and higher ammonia excretion rates than oysters in the LSU cohort, across ploidy. D ifferences between how hatcheries spawned each cohort, such as  the larger number of broodstock parents used to spawn AUSL oysters,  could have contributed to  the differences  observed in physiological parameters. This points to the importance of tracking  multiple  factors such as pedigree and which hatchery an oyster originated from when developing repositories.