PROGRESS IN BIOLOGICAL INQUIRIES, 193 4 379 



of the parasite miuI mIso allow iiion^ favorable <i:ro\vin<i; conditions for 

 those whieh art' heavily infected. Investi<^ations are b('in<j^ continued 

 at the lieaiifort laboratory for the i)urpose of deterniinin<^ the life 

 cycle, method of tlistribution, and proper identiiication of this micro- 

 organism which appears to be a new natural enemy of the oyster 

 of considerable economic importance. 



OYSTER IN>T.STIGATIONS IN WASHINGTON 



For a number of years the Olympia oyster industry has had dif- 

 ficulties due to unsatisfactory catches of seed 03'sters. Although the 

 quality of the product has been normal the growers were unable, by 

 use of the usual methods, to collect spat enough to fill the beds. 

 For this reason an investigation of the spaw'iiing and setting habits 

 of this species of oyster was undertaken by Dr. A. E. Hopkins. Dur- 

 ing four seasons accurate data have been collected on various phases 

 of the problem, and the cumulative results are becoming constantly 

 more significant. In addition, the rapid expansion of the Japanese, 

 or " Pacific "', oyster industry has involved numerous problems, such 

 as propagation of this species in American waters, effect of environ- 

 mental factors on fattening, and so forth. 



Experimental studies have been carried on in typical oyster- 

 growing areas of the most important bays near Olympia. Three 

 times weekly during the breeding season 100 adult oysters {Ostrea 

 luj^da) were opened on each of the test becis, and the larvae from 

 gravid specimens preserved for laboratory study. In this manner it 

 was learned that larvae develop for about 10 days in the maternal 

 brood chamber before being cast out into the open water. The data 

 also show accurately the time and intensity of spawning in each 

 localitj' throughout the season, as well as the total amount of spawn- 

 ing taking place. For example, in Oyster Bay in 1932 all of the 

 oysters produced larvae once and 75 percent of them produced second 

 broods. In 1933 only about 75 percent spawned as females, and in 

 1934 between 90 ])ercent and 100 percent did so. These results indi- 

 cate that there is wide variation between different seasons in the num- 

 ber of times spawning occurs, and consequently in the potential seed 

 catch. 



The time of beginning of spawning is clearly determined by tem- 

 perature. During each season the first gravid specimens were found 

 when the average daily water temperature reached 13° to 14° C. 

 Records for the past 3 years show that the interval between spawn- 

 ing and setting varied between 39 and 51 days, of which the first 10 

 days represent development within the maternal brood chaml)er. 



By careful analysis of the time and intensit}^ of setting throughout 

 the season it has been found that in certain bays periods of setting 

 occur at intervals and are associated with the tidal cycles. This was 

 found during previous years, and the 1934 results furnish further 

 confirmation. Attempts have been made to determine in what num- 

 ner the tidal cycle is effective, but the problem requires further experi- 

 mentation. Although setting is heaviest during a run of extreme 

 low tides, actual attachment of the larvae does not occur when the 

 tide is low but appears to take place primarily at relatively high tide. 

 Whether copper in the water is the effective agent for this species 

 has not yet been determined. 



