30 U. S. BUREAU OF FISHERIES 



to the cause of spat mortality could be obtained. This survival coin- 

 cided with an absence in the bay of the black muck that generates 

 hydrogen sulphide, and which was so prevalent in 19:21. when heavy- 

 mortality occurred. This tended to support the hypothesis that 

 the hydrogen sulphide generated on the bottom was a principal 

 cause of spat loss. Valuable data in regard to larval life history 

 and the effects of temperature on spawning were obtained. 



About Milforcl. Conn., a fairly good young set was almost entirely 

 lost while still minute. Search and inquiry in September showed a 

 quite generally distributed but (except in a few favored places) very 

 light set. The increased oyster planting on inshore lots, as ad- 

 vocated by the bureau, is believed to have helped matters. At Mil- 

 ford the work of testing the effect of materials occurring as pollut- 

 ants was continued. Salts of copper, zinc, and lead were used. As 

 in previous trials, copper proved most deadly. Young oysters placed 

 in a solution containing 1 part of copper per million were killed, so 

 that but 30 per cent survived after 5 days. In a solution containing 

 2 parts per million all died within 4 days. In the controls nearly 

 complete survival occurred. Solutions of zinc and lead salts of 10 

 parts of the metal per million exhibited no greater toxicity tlian did 

 solutions of 1 and 2 parts of the copper per million. In the case 

 of large larvse solutions of copper salt in strengths varying from 

 10 to 0.5 parts of copper per million and of zinc and lead in a 

 strength of 10 parts per million proved fatal in less than a day. In 

 the controls the greater portion of the larvse lived into the second day. 



The services of J. W. Sale, chemist in charge Water and Bever- 

 age Laboratory, Bureau of Chemistry, were obtained from the 

 Department of Agriculture. Mr. Sale investigated the Housatonic 

 River, New Haven Harbor, and Hammonasset RiA'er. principally for 

 heavy metals. Hammonasset River, comparatively free from jjollu- 

 tion, showed no trace of copper or zinc, both of which were found 

 in considerable quantities in the other waters. Copper was found 

 in both the Housatonic River and New Haven Harbor in quantities 

 approaching those which experiments indicate are deadly to oyster 

 larva?. 



Experiments in a new method of artificially propagating the 

 oyster were carried on during the summer of 1923 by H. F. Pry- 

 therch at the plant of the Connecticut Oyster Farms at Milford, 

 Conn. The objects of this work were (1) to determine by a series 

 of experiments the important environmental conditions required by 

 the oyster larvae for normal growth and development: (2) to raise 

 a small number of the larvae under controlled conditions during the 

 free-swimming period until they " set," and (3) to perfect the method 

 so that oysters may be raised from the egg in sufficiently large num- 

 bers to make the process one of commercial value. 



The new method proved successful in an experimental way from 

 the start, and tAvo batches of oysters were raised from the eggs 

 under artificial conditions. This success was attributed to the close 

 imitation of natural conditions. In the first place, millions of fer- 

 tilized eggs were obtained by allowing the adult oysters to spawn 

 naturally under favorable conditions and not by cutting them open 

 and stripping the apparently ripe eggs and milt from them. As 

 soon as the eggs developed into tiny swimming oyster larv?e they 

 were reared in tanks of running water for 15 to 20 days until they 



