436 ^- S- BUREAU OF FISHERIES 



contain niatnre ova. The animals, formerly functioning as males, 

 have now reached the stage of functional females. 



The adults are, with few exceptions, of separate sexes. Among 

 several hundred mature clams studied by means of serial sections 

 only two cases of functional hermaphroditism have been observed. 

 Nevertheless, examination of gonads of adult males reveals in almost 

 every instance the presence of small oocytes somewhere along the 

 Avails of the follicles. This may indicate the potentiality of chang- 

 ing the sex even in the adult condition, but so far there has been 

 no evidence obtained to warrant such a conclusion. 



Spermaries of adult males contain mature spermatozoa at all 

 seasons of the year. When placed in sea water spermatozoa begin 

 to swim actively in their typical spiral way after 2 to 3 minutes 

 of quiescence. This simple experiment was tried at biweekly inter- 

 vals throughout the year and always with positive results. The 

 ovaries of adult females also contain large ova at all seasons of 

 the year. In fact, little difference will be noted on superficial exam- 

 ination of samples collected in December and June. In both cases 

 the follicles are large, distended, and filled with large oocytes. In 

 this respect the quahog differs remarkably from the American oyster, 

 in which only shrunken follicles are found during the autumn and 

 Avinter. 



To study the effect of water temperature on the feeding of qua- 

 hogs experimental animals Avere kept under natural conditions in 

 large tanks in Avhicli the Avater Avas rencAved with every tide. Each 

 clam Avas immobolized by imbedding one of its A'alves in a mixture 

 of cement and sand, and connected to the leA'er of a recording ap- 

 paratus placed about 10 feet aboA'e. Each moA-ement of the shell was 

 recorded on the chart, and the temperature of the Avater was at the 

 same time recorded by a thermograph. The clams Avere kept at- 

 tached to the recording apparatus for varying periods of time rang- 

 ing from 1 to 10 daA'S. Usually the records of two clams Avere taken 

 simultaneously. During these experiments the Avater temperature 

 in the tanks varied from 0.0° to 28.0° C., thus coA^ering the entire 

 natural range of temperatures to Avhich clams are subjected. 



The hibernation of clams occurs Avhen the water temperature is 

 4.9° C. or loAver. Prolonged periods of opening of the shells and 

 presumably actiA^e feeding and respiration proceeds at temperatures 

 of 6.0° C. and above. This knoAvledge of the effect of temperature 

 on the shell activities of the clam may add to a better understanding 

 of several practical problems of the clam industry. Undoubtedly 

 groAvth and fattening of clams, as Avell as deA'elopment of sexual 

 products, are dependent upon the length of time the shells are open 

 because feeding can take place only during that time. 



INVESTIGATIONS ON AQUICULTURE 



H. S. Davis, in charge 



luA'estigations on problems relating to aquiculture were continued 

 along much the same lines as in 1934. Greater emphasis, hoAvever, 

 Avas placed on field studies since it Avas believed that it Avill be im- 

 possible to utilize the products of our hatcheries to best advantage 

 until Ave learn more about the various factors that affect fish in 



