The American or Eastern Oyster 



By 



VICTOR L. LOOSANOFF. Senior Scientist 



Bureau of Commercial Fisheries 

 Tiburon, Calif. 



INTRODUCTION 



The American or, as it is more often called. 

 Eastern oyster is the oyster of commerce of 

 our Atlantic and Gulf of Mexico coasts and is 

 also sold in small quantities on the Pacific 

 coast. Its scientific name is Crassostrea 

 virginica, and it is a true oyster, being a 

 member of the Phylunn MoUusca, Class 

 Pelecypoda, and Family Ostreidae. True 

 oysters are distinguished by having dissinnilar 

 lower and upper shells, by attaching the left 

 shell to a substratum, and by having no traces 

 of foot and byssus in adults. Their shell liga- 

 ment is a band between the two valves which 

 may be of triangular shape. 



Altogether, more than one hundred living 

 species of oysters have been described, but 

 only a few are of economic importance. Most 

 oysters occur between tidal levels or in shallow 

 waters of estuaries, but some species live in 

 depths of several thousand feet. They are en- 

 countered along the temperate and tropical 

 coasts of all continents. 



In addition to the Eastern oyster, two other 

 commercial species are cultivated in this 

 country. One is the Japanese or, as it is now 

 called. Pacific oyster, Crassostrea gigas , 

 grown on the west coast, principally from im- 

 ported seed: the other is the Olympia oyster, 

 Ostrea lurida , a native of the Pacific coast. 

 In 1949, the European flat oyster, O. edulis , 

 was introduced into New England and now is 

 found occasionally in Maine waters. Recently, 

 small numbers of hatchery-grown oysters of 

 this species have been used in planting experi- 

 ments in California. 



The Ajnerican oyster (fig. 1) is ^videly dis- 

 tributed and in some areas is extremely 

 abundant. It is found from Massachusetts 

 south along the eastern coast of the United 

 States and also along the Gulf of Mexico 

 coast. Some groups still live in the waters of 

 Maine and New Hampshire where they were 

 considerably more abundant several decades 

 ago. The Annerican oyster is also cultivated 

 in Canadian waters, principally in the shallow 

 southern part of the Gulf of St. Lawrence. 



The Pacific oyster is imported as seed 

 from Japan and grown in large quantities 

 in Puget Sound, Willapa Bay, and Grays 

 Harbor in Washington, and also in Humboldt, 

 Tomales, and Drakes Bays of California. Small 

 quantities of Pacific oysters are also grown 

 in certain protected inlets along the Oregon 

 coast. It was first imported to the United 

 States on a commercial scale in 1905, but 

 during the last 3 decades its production has 

 rapidly increased and now constitutes about 

 15 percent of the total annual yield of oyster 

 meats in the United States. It is a large, 

 rapidly growing moUusk, anatomically and in 

 general appearance closely resembling the 

 Eastern oyster. 



The Olympia oyster, a native of the Pacific 

 coast, is found from Charlottestown, British 

 Columbia, to San Diego Harbor, Calif. It 

 occurs in greatest numbers in Washington, 

 especially in the lower part of Puget Sound. 



ENVIRONMENT 



The American oyster (hereafter referred 

 to only as oyster) is adapted to live in waters 

 with considerable variations in salinity and 

 temperature. Its optimum salinity range is 

 roughly from 10.0 to 28.0 parts per thousand 

 (p.p.t.) or, in other words, in ■water containing 

 about 1.0 to 2.8 percent sea salt. The oyster 

 can survive in the open ocean for some time, 

 but usually it does not reproduce or grow well 

 there. It also can survive periods of spring 

 floods or heavy rains when the salinity of the 

 water is abnormally reduced. In such instances, 

 however, the temperature is an extremely 

 important factor in survival because the lower 

 the temperature, the longer the oysters can 

 live in water of low salinity. For example, 

 experiments have shown that when the water 

 temperature is only about 50° F. many oysters 

 can survive exposure to a salinity of 3.0 p.p.t. 

 for 30 days. 



Oysters in Long Island Sound, where salinity 

 of the water is about 28.0 p.p.t., fed even when 

 placed in water of reduced salinity, sometimes 



