Specific pathogen free culture of the Pacific oyster (Crassostrea gigas) in a breeding research program: Effect of water treatment on growth and survival

A specific pathogen free (SPF) filtration system was built to exclude Haplosporidium costale, Seaside Organism (SSO) from the Pacific oyster (Crassostrea gigas) hatchery and nursery of the Molluscan Broodstock Program at Hatfield Marine Science Center in Newport, Oregon. Since its inception in 1999, all groups of Pacific oyster seed produced have tested negative for SSO or any other certifiable infectious agent under histological examination. Microparticle filtration to 1 μm, further filtered to 0.35 μm for larvae, or in combination with ultraviolet sterilization, for juveniles was used in the system to exclude SSO from seawater drawn from Yaquina Bay, where it is a resident. The SPF water had negative effects on larval and juvenile oyster growth, and juvenile survival. A series of experiments assaying different water treatments was conducted in order to remedy these effects. The addition of calcium bentonite and calcium montmorillonite significantly improved larval growth over filtered water alone in multiple experiments, increasing the growth of larval cultures by as much as 33% at a dose of 5 ppm day− 1. These two clays' adsorptive qualities are likely responsible for their beneficial effects. Effects of clay additions to SPF water on juvenile oyster growth were less pronounced and less temporally consistent than in larvae. Clay additions that benefited larvae did not always result in a significant increase in seed growth. Our short-duration seed experiments with clay additions showed that calcium bentonite at a dose of 2 ppm day− 1 inconsistently resulted in significant improvement in seed growth compared with SPF water with no clay addition.