Rearing of the native Pacific Coast oyster larvae, Ostrea lurida Carp., under controlled laboratory conditions Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/nc580p45h

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  • Fisheries Laboratory during 1952, in the rearing of the native Pacific Coast oyster, Ostrea lurida Carp., in small containers. The decline of the oyster fishery in Yaquina Bay, Oregon, has been attributed in part to the lack of adequate spat-falls. Investigations were begun in 1947 to devise methods of artificially rearing oyster larvae under controlled conditions which might later be extended in producing seed oysters in adequate numbers for the commercial production of the native oyster. Adult oysters from which larvae were obtained for the rearing tests were Longed from the native oyster beds near Oysterville on Yaquina Bay. The larvae were taken from the adult oyster by two methods. The adult oysters were placed in five-gallon wide-mouth jars and the temperature raised to 200 C. until natural swarming occurred, or the adult oysters were opened manually and the larvae were taken from the gravid oysters. These methods apply during the natural spawning season of the native oyster which occurs in late spring and summer. The rearing containers used were five-gallon wide-mouth jars and 12-gallon crocks. The larger containers gave better results. A filtering device was installed in each container to accomplish the water change without loss of larvae. A rearing temperature of 18 to 200 C. was maintained by controlling the room temperatures. All salt water used in rearing experiments was sand filtered to remove organisms that may prey on the larvae or take food in competition with them. Larval food consisted of plankton which measures less than 9 microns. These organisms were cultured in small containers and 25 ml. of the media was introduced into the rearing containers every 48 hours. Rearing containers with various larval concentrations received the same amount of media and the results showed no indications of over or under feeding. A salinity range of 26 to 32 parts per thousand yielded satisfactory results. The upper and lower limits were not determined. When the bay salinity exceeded 34 parts per thousand, the salinity was reduced by adding fresh water. This resulted in larval mortality. The reason for this mortality was not determined but it is possible that the fresh water used was toxic. The water in the rearing containers was changed every other day in the early experiments. A less frequent water change was tried which yielded satisfactory results. A water change once or twice during the larval free-swimming period appears to be adequate. The larval growth rate was measured and a daily growth of 4 to 5 microns is considered satisfactory. The rate of growth appears to be a reliable indication of the condition of the larvae. The larvae set out on a cultch after a 15 to 25 day free-swimming period. Setting began when the larvae measured about 260 microns. The spat received the same care as the free-swimming larvae and considerable 2 shell growth was evident. During the winter months, induced spawning was investigated. Adult oysters were taken from the bay and held in the laboratory at a temperature of 18 to 200 C. The water was changed occasionally and media was added. Some spawning occurred after the oysters were held for 6 to 8 weeks. The larvae thus obtained were successfully reared to the setting stage.
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