Aquaculture demands for high value products, like the Eastern oyster (Crassostrea virginica), continue to rise. Many factors, including eyed larval production, limit commercial oyster output. To combat this, hatcheries spawn diploid females with tetraploid males to produce triploid offspring, which in many instances exhibit faster growth than diploid oysters and maintain meat quality during the reproductive season. Despite improvements, gametes produced in hatcheries are often of low quality. While it is known that abiotic factors, like temperature and pH, influence gametogenesis in Eastern oyster the effects of salinity need to be fully identified. In C. gigas low salinity negatively impacted fertility, which indicates inhibition in sperm motility. To expand on these ideas, this study investigates how salinity affects Eastern oyster gametogenesis and gamete quality for triploid production. Oysters were conditioned in recirculating aquaculture systems (RAS) at 10, 20, and 30 PSU for 30 days. Temperature and light mimicked oceanic conditions in the Gulf of Mexico. RAS contained 6 ×140 L tanks, each housing 15 oysters per ploidy. Oysters were opened and sex determined by observation of their gonads under a microscope. Semen was collected from tetraploid males, sperm density was determined using hemocytometer counts while viability was evaluated by flow cytometry. Sperm velocity (VCL) and motility were evaluated by computer assisted sperm analysis. Eggs collected from diploid females were assessed for fecundity and egg size. For both sexes, lipids were extracted and analyzed by gas chromatography. Histology samples will be processed and gametogenic development assessed based on a maturity stage index.
Sperm density tended to increase at higher conditioning salinities (1.35×109 at 10 PSU to 1.86×109 sperm/mL at 30 PSU), however this trend was non-significant. At 30 and 60 s post-activation of sperm, oysters conditioned at 10 PSU had lower VCL than other salinities (Fig 1A). Sperm motility was lower for oysters conditioned at 10 PSU (Fig 1B). Conditioning salinity also affected sperm viability with lowest values observed at 30 PSU (Fig 1C). Female fecundity tended to decrease when oysters were conditioned at higher salinities (2.74×106 at 10 PSU to 2.41×106 eggs at 30 PSU), however this trend was non-significant. Results, thus far, suggest 20 PSU as a promising conditioning salinity for sperm quality. Lipid and histology analyses will provide further support for this conclusion.