612 V. S. BUREAU OF FISHEEIES 



OYSTER INVESTIGATIONS 



Oyster investigations during 1930 were continued under the direc- 

 tion of Dr. Paul S. Galtsoff along the f oUowing lines of research : 

 Experimental studies in oyster culture, studies of the causes of the 

 decline of the oyster industry and of the mortality of oysters, analy- 

 sis of the oj^ster bottoms, and development of the methods of con- 

 trolling the enemies of the oyster. 



Field and laboratory research work was carried out both along 

 the Atlantic and the Pacific coasts of the United States and, at the 

 request of the Territorial government of Hawaii, was extended to 

 the Hawaiian Archipelago. 



SETTING, METAMORPHOSIS, AND DISTRIBUTION OF OYSTERS 



During the past summer the investigations of the physical, chem- 

 ical, and cytological aspects of the setting of the oyster 

 have been completed by H. F. Prytherch. These studies have shown 

 that copper is the specific factor of greatest importance in the at- 

 tachment, survival, and distribution of this marine organism. Cop- 

 per is brought down to the inshore coastal areas either by the rivers 

 or by the flow from underground channels and examination of sev- 

 eral fresh-water streams in Connecticut has shown that it is present 

 in these waters in amounts varying from 0.1 to 1.5 parts per mil- 

 lion and is present in greatest amounts after periods of heavy 

 precipitation. 



Since the setting of the oyster larva may be induced by solutions 

 containing as little as 1 part copper to 50,000,000 parts of sea 

 water, it is not surprising to find that there is a definite relation be- 

 tween the distribution of oyster beds and prolific seed producing 

 areas, and the flow of fresh water containing copper into these 

 coastal regions. In Milford Harbor, Conn., setting takes place at 

 low slack water when copper was found to be present in amounts 

 varying from 0.1 to 0.6 part per million and did not occur at other 

 stages of the tide when it was impossible to find measurable amounts 

 of this metal. Traces of copper were found to be necessary also 

 for the metamorphosis of the larva into a spat and this served to 

 bring about the breaking up of the pigment spots and the release 

 of numerous deeply colored cells of which they are formed. In the 

 absence of copper the attached larva failed to metamorphose or 

 grow and lived for a period of 8 to 14 days. Those receiving copper 

 stimulation after attachment became transformed into spat in a few 

 hours and grew rapidly under the same conditions as those used for 

 the retarded individuals. 



The salinity of the water was found to have a pronounced effect 

 upon the velocity of the setting reaction or length of time required 

 for attachment. The optimum condition for setting was found to be 

 in salinities from 15 to 20 parts per thousand, while above or below 

 this salt concentration the reaation was gradually retarded and 

 finally required several hours for completion in salinities above 30 

 or below 5 parts per thousand. 



The beneficial and stimulative value of minute amounts of copper 

 must not, however, be construed to indicate that trade wastes contain- 



