The goal of this study was to compare growth and survival of eastern oysters (Crassostrea virginica) reared in silo and bottle upwellers. Oysters were maintained in their respective nursery systems until reaching R2 (retain on a 2 mm screen) at which point they were moved into the field to an adjustable longline system. Biweekly, oysters were measured (height, length, width) and mortalities estimated. Stocking density was reduced at each sampling point by removing slow growers. Sampling continued for six weeks. At the end of the trial, oysters were examined for backbend deformities.
Following the nursery period, silo reared oysters had greater shell height and length but a lower fan ratio than those reared in bottles. After 6 weeks, silo reared oysters reaching R22 or larger had greater shell height and width than bottle-reared oysters of a similar size (Table 1). Oysters between R16 and R22 from silos were significantly longer than those from bottles. Both rearing strategies resulted in equal proportions of oysters in each size class (Fig. 1) with equivalent cup ratios. R22 oysters from silo nurseries had higher Fan ratios after 6 weeks. There were no differences between rearing groups in mortality or deformities (i.e., backbends) after 6 weeks.
Overall, silo upwellers resulted in faster oyster growth than bottle upwellers. The size benefit was most apparent in the fastest-growing oysters. Size differences were generally small; therefore, optimization of bottle upweller parameters (i.e., water flow, stocking density, etc.) may reduce growth differences between these two nursery types.