Graduate Thesis Or Dissertation
 

Effects of temperature, salinity, feeding, substrate, and storage on the setting and survival of commercially-reared eyed larvae of the Pacific oyster, Crassostrea gigas

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  • A series of factorial experiments were conducted using eyed oyster larvae (Crassostrea gigas) reared at a commercial hatchery in Netarts, Oregon. The objectives of the study were to obtain the highest percentage of setting larvae and the best survival of the spat. Experiments on the combined effects of temperature and salinity indicated that temperature had a highly significant effect on the setting of Pacific oyster larvae. For temperatures ranging from 15°-30°C, the percentage of larvae setting during a 48-hour period increased as temperature increased. There was no significant difference in setting for salinities ranging from 15-30 ppt. In one setting experiment with Kumomoto larvae (a different variety of C. gigas), the differences among the sixteen combinations of temperature and salinity were statistically insignificant. Feeding larvae 120,000 cells per milliliter of the alga Pseudoisochrysis paradoxa did not significantly improve setting during a 48-hour period, and in one experiment temperature and feeding interacted to the detriment of setting. There was no significant difference in the percentages of attaching larvae when oyster, cockle, or butter clam shells were used as substrates. Dipping oyster or butter clam shells in an aqueous extract of oyster tissue improved setting, but the presence of the extract did not improve setting on razor or littleneck clam shells. Storing eyed larvae at 5°C for several days before setting them appeared to increase the percentage of attaching larvae. The best temperature for setting stored larvae was 25°C. Oyster larvae that attached to shell cultch during the setting experiments were held in a tank of raw seawater in the laboratory. After eight to nine months, the percentages of surviving spat were calculated. Survival was poor for larvae set at 15°C, and there was some evidence of higher mortality among larvae stored for several days before being set. Because of the laboratory conditions, these studies may not have provided a realistic measure of spat survival under natural conditions, and field studies should be carried out to confirm these results.
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