ADAPTATION OF THE FEEDING MECHANISM OF THE 
OYSTER (Ostrea gigas) TO CHANGES IN SALINITY 1 
By A. E. Hopkins, Ph. D., Aquatic Biologist, United States Bureau of Fisheries 
CONTENTS 
Page 
Introduction 345 
Material and methods 346 
Description of experiments 347 
Series I 348 
Series II 350 
Series III 351 
Series IV 353 
Series V 355 
Series VI 356 
Series VII 356 
Discussion 360 
Summary 362 
Literature cited 363 
INTRODUCTION 
Natural beds of oysters are found characteristically in such inshore waters as the 
coastal estuaries and bays in which there is a considerable dilution of the ocean water 
by land drainage. Prytherch (1934), in an extensive monograph describing an experi- 
mental study of the ecology of Ostrea virginica, concluded that successful propagation 
of oysters depends upon the presence in the water of copper ions required by the 
swimming larvae before attachment, or setting, may take place. In nature the copper 
is introduced into sea water in solution in the fresh water of rivers, thereby locating 
natural oyster grounds where they are subject to frequent changes in salinity. 
Referring to 0. virginica, Churchill (1920) stated: 
Oysters are found in water ranging in density from 1.002 to 1.025 (about 2.5 to 33.0 parts per 
mille), but cannot withstand densities lower than 1.007 (9 parts per mille) for indefinite periods. 
In general they seem to thrive best in densities between 1.011 and 1.022 (14.36 to 28.80 parts per 
mille). 
This range apparently refers to areas in which natural oyster beds are located, or 
those areas in which propagation takes place. 
The feeding activities, however, may not be most efficient at the same range of 
salinity or density as in the case of propagation. It may frequently be observed that 
oysters grown on those grounds where seeds are caught most effectively do not fatten 
as well as those grown in different areas. Oyster growers typically catch seeds in one 
place and transplant them to localities which experience has shown to be favorable for 
* Bulletin No. 21. Approved for publication June 4, 1936. 
345 
