tissues are given by Calderwood and Armstrong 

 (1941). 



VARIATIONS IN GLYCOGEN CONTENT 



Glycogen is the reserve material of the oyster. 

 It is stored primarily in the connective tissue of 

 the mantle and labial palps. During the rapid 

 proliferation of se.x cells the reserve supply is used, 

 and by the end of the reproductive cycle the 

 amount of glycogen is at a minimum and the 

 mantle is reduced from a thick heavy layer to a 

 thin transparent membrane. Soon after spawning 

 the oysters begin to form and store glycogen and, 

 in the parlance of oyster growers, become fat. 

 The expression fatness as it is used in trade is a 

 misnomer because it does not refer to an increase 

 in lipids. In New England waters the accumu- 

 lation of glycogen reaches its maximum during 

 late autumn but sometimes continues even in 

 winter. As a rule the glycogen remams at a high 

 level until the beginning of rapid proliferation of 

 sex cells in May. Seasonal fluctuations in glycogen 

 content are common to all the species of oysters 

 that have been studied. The pattern of changes 

 varies in different localities and in difi'erent species 

 depending on local conditions — temperature and 

 abnormal salinity of water, abundance and type 

 of food available, and intensity of feeding. 



Seasonal changes in the glycogen content of 

 New England oysters show a definite cycle related 

 to gonad development and spawning. The rapid 

 increase in the number of sex cells in the gonad 

 e.xhausts the reserve materials and brings the 

 glycogen content to its minimum, which usually 

 occurs immediately after spawning. After a short 

 period of relative inactivity during which the 

 unspawned sex cells are reabsorbed the oysters 

 begin to accumulate and store glycogen in their 

 tissues. The process may be rapid, as for instance 

 in September to December 1933 (fig. 357) or 

 gradual as in the same period in 1934. The 

 glycogen count of oysters of the same population 

 varies from year to year. It can be seen in fig. 

 357 that in 1934 the content of glycogen after 

 spawning was significantly higher than in the 

 preceding year. Microscopic examination of these 

 and Cape Cod oysters showed that sometimes the 

 glycogen reserve is not depleted during the growth 

 of the gonad and remains at a relatively higli 

 level throughout the spawning season. Another 

 interesting fact noticeable in the annual glycogen 

 curve is the continuing increase in glycogen during 

 the cold months of winter when feeding ceases. 



J I I I I \ I I I I I I I I I 1 I I I L_ 



Figure 357. — Glycogen and water content of adult 

 oysters (5-years-okl in 1933) from commercial oyster 

 bed off Charles Island, Long Island Sound. 



The amount of glycogen stored in the tissues at a 

 given moment is the balance resulting from the 

 glycogen formed (glycogenesis) and that broken 

 down (glycolysis) . Biochemistry of both processes 

 known in great detail in mammals, has not been 

 adequately investigated in bivalves. It appears, 

 however, reasonable to postulate that the tissue 

 glycogen continues to be synthesized by the 

 oyster from the carbohydrates accumulated with 

 food during the period of active feeding or from 

 indigenous sources of intermediary metabolism. 



Increase in glycogen content is usually associ- 

 ated with an increase in solids and a corresponding 

 decrease in water. There are, however, unusual 

 instances as in the oysters found in November and 

 December 1933 (fig. 357) which had a higli glyco- 

 gen content in spite of an increase of water to 88 

 percent and corresponding loss of solids. 



The annual glycogen cycle in oysters of the 

 York and Piankatank Rivers, Va. (GaltsofF, Chip- 

 man, Engle, and Calderwood, 1947) follows the 

 general pattern simihir to that of Long Island 

 with the only diff'erence that the lowest concen- 

 trations were observed in July to September and 

 the highest in November to February. In Loui- 

 siana the period of low glycogen was found by 

 Hopkins, Mackin, and Menzel (1954) to extend 

 from April to the end of November. All the dif- 

 ferences mentioned above are associated with the 

 longer reproductive periods in warmer climates. 



The cyclic change in glycogen content has been 

 described for 0. edulis and C. angulaia by Bierry, 

 Gouzon, and Magnan (1937); Bargeton (1945); 



386 



FISH AND WILDLIFE SERVICE 



