Salinity and temperature tolerance of embryos and juveniles of the pearl oyster, Pinctada imbricata Röding

The responses of embryos and juveniles of the pearl oyster, Pinctada imbricata, to variation in temperature and salinity were investigated to assist hatchery production and farming. Embryos were incubated at temperatures in the range 14-26°C and salinities in the range 11-35 ppt. Embryos did not develop to D-veliger stage at 14°C and at salinities of 26 ppt or less. Within the salinity range 29-35 ppt, the percentage embryos developing to D-veliger stage increased significantly with increasing salinity. Within the temperature range 18-26°C, increasing temperature increased the rate of development as well as the number of embryos developing to D-veliger stage within 40 h. Juvenile P. imbricata (17 mm shell height) held at temperatures in the range of 14-24°C were exposed to salinities in the range of 11-35 ppt. Spat formed byssal attachments most rapidly at salinities of 29 and 32 ppt, irrespective of temperature. At these salinities, >70% of oysters formed byssal attachments to the aquaria walls within 6 h. Outside this narrow salinity range, the rate of byssal attachment decreased and ceased altogether at salinities of 17 ppt or less. Temperature also affected byssal attachment although the impacts were not as great as those of salinity. Within the optimal salinity range (29-32 ppt), the rate of byssal attachment was fastest at 18°C, where up to 80% of oysters had attached within 4 h. This rate was slightly greater than that observed at 22°C, which in turn exceeded those observed at 14 and 26°C. Salinity and temperature also affected survival. Irrespective of temperature, survival was high at salinities of 32 and 35 ppt. By contrast, high rates of mortality occurred within 7 days at salinities of 23 ppt or less. Onset of mortality was most rapid and overall mortality highest at the two extremes in temperature tested, 14 and 26°C.