Ecotoxicological evaluations of common hatchery substances and procedures used in the production of sydney rock oysters Saccostrea glomerata (Gould 1850)

Progress in the Sydney rock oyster Saccostrea glomerata industry, through the adoption of oyster spat selected for faster growth and disease resistance, has been hampered by long-term variability in commercial hatchery spat supply. As part of a broader study to evaluate spat production impediments, the chronic toxicity of substances commonly used in bivalve hatcheries and the effects of handling procedures during early ontogeny (embryo to D-veliger) were evaluated. Among the substances tested, chlorine, Virkon S and Virkon S for Aquaculture (virucidal disinfectants, Antec International Limited, Suffolk, UK), bore water and stored rainwater were found to significantly affect larval development at practically/commercially-relevant concentrations. Toxicity was determined by quantifying embryo-larval development after 48 h exposure and three tests were performed for each substance or procedure. Concentrations of 0.83-1.66 mg L ^-1 of chlorine in seawater and 0.05-0.5 mg L^-1 of Virkon S in seawater significantly decreased the normal development of embryos after 48 h exposure. An EC₅₀ value of 0.76-1.18 mg L^_1 for chlorine in seawater and 0.47-1.01 trig L^_1 for Virkon S in seawater was derived. The EC₅₀ value for Virkon S for Aquaculture was 0.99-1.12 mg L^-1 and this substance caused significant development problems for larvae at a concentration of 0.5 mg L^-1 in seawater. Tests that added stored rainwater to seawater had a significant decrease in the percentage of embryos developing to the D-veliger stage at concentrations greater than 1%, whilst no effect was detected at 0.1%. The EC₅₀ value for rainwater was 0.67% to 2.29%. Similarly, bore water added to seawater caused a significant decrease in the percentage of embryos to develop to the D-veliger stage at a concentration of 10% and no effect was observed at 1%. The EC₅₀ value for bore water ranged between 2.3 and 3.7%. Handling procedures for screening fertilized eggs did not significantly decrease development percentage after 48 h incubation time. Likewise, tests conducted with de-ionized water at concentrations up to 10% added to seawater did not significantly reduce the percentage of embryos to develop to the D-veliger stage after 48 h exposure. This study highlights the sensitivity of S. glomerata larvae to surfactants and disinfectants and identified contaminated water sources.