PROGRESS IN BIOLOGICAL INQUIRIES, 1934 373 



tions conducted by the United States Corps of Engineei-s. On many 

 occasions the oystiM- njrowors of the district called upon the laboratory 

 at Milfortl for information and advice concerning various problems 

 of oyster culture. 



The major part of the work was a continuation of the investiga- 

 tion on the growth and fattening of oystei-s started by the Bureau 

 in the spring of 1932. It consisted mainly of a study of environ- 

 mental conditions and seasonal changes occurring in oysters. By 

 comparing the temperatures of the water for the last 3 years, two 

 points of great biological interest and significance become apparent: 

 First, the duration of the hibernation period and the activity of the 

 oysters vary, but within very narrow limits. During the years 1932, 

 1933. and 1934 the oysters hibernated 155, 160, and 149 days, respec- 

 tively; second, the spawning period, that is, the number of days 

 per year when the temperature of the water remained above 70° F., 

 was'42 in 1932, G9 in 1933, and 59 in 1934. It is interesting to note 

 that the shortest pei-iod of hibernation occurred in 1934 regardless 

 of the temjierature during this year. The spawning period of 1932 

 constituted only about 60 percent of that in 1933. 



From the observations on phosphates it becomes evident that the 

 utilization and regeneration of these nutrient salts in Long Island 

 Sound is a definite cyclic process with a minimum amount present 

 in the water during the warmest part of the year and a maximum 

 amount occurring in winter. The temperature of the water and 

 solar radiation are the two principal factors controlling the phos- 

 phate cycle, which in turn determines the fluctuations in the abun- 

 dance of plankton. Analysis of river water showed that it is very 

 poor in phosphates and contributes very little to the phosphate 

 reserve of the Sound. 



Observations on the growth of oysters show that they continue to 

 increase in length and weight throughout the entire year, including 

 the winter months. The rate of growth gradually decreases with 

 age. In 1932 the average increase in length of 4-year-old oysters 

 planted on expei-i mental beds at Charles Island was about 2 cm, in 

 1933 it amounted to 0.9 cm, and during the last year it did not exceed 

 0.5 cm. Changes in the increase in total weight are even more strik- 

 ing. In 1932 the increase in total weight of 4-year-old oysters was 

 72 percent, in 1933 it was only 40 percent, and during the last year 

 less than 10 percent. Thus, tlie self -inhibiting phase of growth— that 

 is, the phase during Avhich the rate of growth decreases with the 

 increase in size or weight of the organism — is very pronounced in 

 the 6-3'ear-old oysters. The weight of the shells of oysters examined 

 during the year constitut<'d from 72.9 to 82.5 ]jercent of total weight, 

 the average. 77 percent, being almost identical with that obtained in 

 1932 and 1933. 



During the year the weight of the meat constituted from 10 to 

 13 percent of total Aveight, the mininnun occurring after spawning; 

 that is, in August-September. 



Observations on the glycogen and mineral content of the oysters 

 were continued. Of the 199 samples of oyster meats collected during 

 the course of the investigations 45 were"^ analyzed for iron, copper, 

 manganese, and zinc. 



