To supplement traditional oyster farming, alternative oyster a quaculture (A OC) has been promoted in the northern Gulf of Mexico during the last decade. Alternative oyster aquaculture is based on the use of off-bottom grow-out methods, hatchery-produced seeds, and selected seedstocks. Most of the seedstock used in AOC are triploids because of their faster growth. In 2016, oyster farmers in Louisiana and Alabama observed unexpected high mortalities of unknown cause. T riploid mortality was also reported by the aquaculture industry in the Chesapeake Bay. To potentially explain causes of triploid mortality, the physiology of diploid and triploid oysters was compared in this study. Diploid and triploid crosses were spawned at two hatcheries ; the Auburn University Shellfish Lab (AU) and the Louisiana Sea Grant Oyster Research Lab (LSU). The diploid cross consisted male and female diploid oysters from Sister Lake . The triploid cross consisted of female diploid oysters from Sister Lake and a male tetraploid line ( 4MC18 at AU , 4DGNL17 at LSU). Oysters from each hatchery constituted the AU and LSU hatchery cohorts.
Clearance rates, absorption efficiencies, routine (fed) and basal (starved 1 week ) oxygen consumption rates , ammonia excretion rates, P. marinus infection intensities, valve movement, and mortality rates of oysters from each ploidy and hatchery cohort were measured. Triploid oysters had higher clearance rates, P. marinus infection intensities (Figure 1) , and mortality than did diploid oysters. Oysters from the AU cohort had higher basal oxygen consumption rates (Figure 2 ) and ammonia excretion rates than oysters in the LSU cohort. No differences in valve movement or absorption efficiency were found between ploidies or cohorts. Ploidy differences suggest better physiological performance of triploids than diploids based on clearance rate and SFG results . However, based on the physiological factors measured, the cause of triploid mortality remains unclear. Repository storage of cryopreserved genetic material and associated biological information can support further efforts to explain triploid mortality by allowing for fu ture studies on specific crosses and gathering results in a centralized location .