Effects of genetic line and stocking density on triploid Crassostrea virginica performance in novel deepwater aquaculture gear

Oyster aquaculture in deep (>6 m) Delaware Bay waters offers a unique opportunity to enhance production, although expansion offshore prevents use of traditional nearshore growing technologies, such as rack-and-bag techniques. Challenges such as inclement water conditions, biofouling, and the costs of gear and stock maintenance hinder the successful production of high-quality oysters for half-shell markets in deepwater aquaculture. One Delaware Bay oyster farm patented a bottom-deployed gear design specifically to employ the high tidal energy present in this estuary to autonomously rotate cages holding the stock. The novel design offers the potential to reduce husbandry frequency, thereby enhancing operation efficiency and reducing labor costs, but performance of this new gear type has not been documented scientifically. Performance of various triploid seed lines (DEBY, NEH, and LOLA) at low and high cage stocking densities (150 and 200 oysters per basket, respectively) were compared to evaluate performance in this recently developed subtidal gear. Performance metrics included final dimensions, growth, condition, shell shape (fan and cup ratios), condition index, mortality, and disease prevalence. Analyses of variance (ANOVAs) indicated that genetic line imposed a significant (P ≤ 0.05) effect on most metrics, which likely resulted from differential sizes across lines at the onset of the experiment. Interestingly, stocking density did not impose a significant influence on oyster size, shape, or mortality. Overall, DEBY and LOLA lines outperformed the NEH lines in most morphometrics. Low density DEBY cages generally exhibited the lower mortality, whereas high density NEH cages generally exhibited higher mortality. Metrics of shell shape and market quality all fell within acceptable aesthetic limits. Along with evaluating genetic line and stocking density effects, this study demonstrates that the novel aquaculture gear evaluated in this study is an effective farming approach for deepwater estuarine settings characterized by relatively high tidal flows. • Performance of three triploid oyster lines (DEBY, NEH, and LOLA) was evaluated at two stocking densities (150 and 200 oysters per cage) in a novel, self-rotating deepwater rearing device. • All triploid lines achieved growth to marketable sizes within 1 year and met favorable shell shape and quality standards for half-shell markets. • Although differences among lines were largely attributable to initial size variation, DEBY stock exhibited the lowest mortality and strongest overall performance. • Stocking density (150 vs. 200 oysters per basket) exhibited no significant effect on size, shape, or mortality, suggesting both densities were within an optimal commercial range.