THE EFFECTS OF ENTRAINMENT PASSAGE ON EMBRYONIC-DEVELOPMENT OF THE PACIFIC OYSTER CRASSOSTREA-GIGAS

Experiments have been undertaken exposing the embryos of the Pacific o yster (Crassostrea gigas) to the key stresses of entrainment within po wer station cooling water systems. The apparatus allowed the testing o f mechanical, thermal, chlorine and pressure effects both alone and in combination. Chlorine levels of between 0.05 and 0.25 ppm Total Resid ual Oxidant (TRO) were found to have a significant deleterious effect on the development of the oyster embryos, with some 50% of larvae show ing abnormal development at 0.05 ppm and 100% suppression of developme nt at levels of greater-than-or-equal-to 0.15 ppm. The pressure regime had a smaller but significant effect, causing a 28% reduction in viab ility. Neither the enhanced temperature caused by the DELTAT across th e condenser tube nor the mechanical stresses of the entrainment treatm ents had any significant effect on larval development. Experiments con ducted under the MAFF protocol for D-stage larval development (at 24-d egrees-C) gave almost identical results to tests undertaken at ambient temperature.