Summary

Ideal salinity and temperature for Sydney rock oysters during early life stages

Sydney rock oysters (SROs) have previously been difficult to rear in large numbers in a hatchery environment.  Oyster larvae would often stop feeding and waste away when raised in tanks.  This meant that the SRO industry could not be supplied with hatchery-produced juvenile oysters that were purposely bred for certain characteristics such as fast growth and disease resistance. A NSW DPI project started in 2003 to investigate ways to better culture SROs in hatcheries.  Part of this project involved testing different salinity and temperature combinations to help overcome larval problems.  SROs were exposed to many different salinities and temperatures when they were at the embryo (0 to 24 hours old), larval (1 to about 22 days old) and spat (juvenile oysters more than 22 days old) stages. This was done to select the best salinity and temperature for survival and growth at each stage.  Various combinations of temperatures between 16 and 30 °C and salinities between 10 and 35 ppt were used.  Most oyster embryos developed at a salinity of 35 ppt and temperature of 26 °C.  The best salinity for growth of larvae was 34 ppt, but this dropped to 26 ppt later in the larval cycle. The best growth of larvae was at warmer temperatures (28-30°C). Larvae survived best at salinities above 26 ppt and temperatures above 20 °C.  Spat grew fastest when both salinity and temperature was at the highest level tested (35 ppt and 30 °C) but had better survival when the salinity and temperature was slightly lower (30 ppt and 23 °C). Spat could not bear salinity levels below 20 ppt.  This work provides hatcheries with the salinity and temperature requirements for SROs at early stages of growth and has contributed to the recent success in reliable commercial scale production of SRO seed.