354 U.S. BUREAU OF FISHERIES 



creasing the food content of the water, and second, to determme the 

 nutritive value of different forms in the oyster diet. Since the 

 understanding of the natural sequence of seasonal changes taking 

 place in the sea is prerequisite for a successful solution of these 

 problems, observations were continued on changes in water temper- 

 ature, chemical composition of sea water, plankton content, and 

 growth and changes in the chemical compositions of oysters. Until 

 the end of July 1933 samples were collected at three stations located 

 in Long Island Sound. Since August 1, observations at 2 stations 

 (lots C18 and 644) were discontinued, because oysters were moved 

 by the owners of these lots to other locations. 



The results of observations made at weekly intervals show that 

 growth of the oyster continues throughout the year even when the 

 organism is in a state of hibernation. During the year the average 

 total weight of 4-year-old oysters, kept on experimental ground at 

 Charles Island in Long Island Sound, increased from approximately 

 150 to 250 grams. The increase continued throughout the year, 

 but there were two periods of accelerated rate of growth, one coincid- 

 ing with the period of gonad formation in June-July, the second one 

 occurring in October-November, at the time of the greatest accumu- 

 lation of glycogen. 



The weight of the oyster shell constitutes from 76 to 81 percent of 

 the total weight of the organism, whereas the weight of its meat 

 fluctuates between 8 and 13 percent. Spawning sharply reduces the 

 weight of the meat from 13 to 8 percent of the total weight, but is 

 immediately followed by a gradual recovery. The maximum weight 

 of the meat was found to occur in November, just before the onset of 

 hibernation. During the period of hibernation there is a gradual 

 xlecrease in the relative w^eight of meat. 



Simultaneously with the observations on oysters, samples of 

 -plankton and water were collected for biological and chemical analy- 

 ;sis. Abundant material, accumulated in the course of the investi- 

 gation, is now being analyzed. 



PREDICTION OF SETTING IN LONG ISLAND SOUND 



Observations on the development of the gonad, started in 1932, 

 were continued in 1933. Samples of oysters, examined in May and 

 June, showed that the amount of spawn to be discharged was far 

 below normal. Oystermen were notified that poor setting was to be 

 expected, and those who, upon receiving this advance information 

 curtailed their planting operations, saved money because, true to our 

 expectations, there Avas no setting in the largest section of Long 

 Island Sound. 



PROPAGATION OF DIATOMS FOR THE ARTIFICIAL FEEDING OF OYSTERS 



Laboratory experiments on plankton as affected by various sub- 

 stances added to sea water w^ere carried out by P. S. Galtsoff, R. O. 

 Smith, V. Koehring, and V. L. Loosanoff. In the majority of the 

 experiments, a pure culture of the small diatom, Nitzchla cIosterm7n, 

 has been used, but attempts were made to isolate other forms which 

 may be useful in artificial feeding of oysters. At present, the follow- 



