ciently rich to warrant commercial exploitation 

 for the manufacture of vitamin D preparations 

 (Bergmann, 1962). 



The cholesterol in bivalves constitutes but a 

 small portion of the sterol mixtures in comparison 

 with those obtainable from gastropods. In C. 

 virginica and C. gigas Bergmann (1934) found a 

 new sterol which he named ostreasterol. Similar 

 compounds found in the sponge Chalina and in 

 Japanese oyster (C. gigas) which were named 

 chalinasterol and conchasterol. Reinvestigation 

 of bivalve sterols proved the identity of ostreas- 

 terol, chalinasterol, and conchasterol with 24- 

 methylenecholasterol (Bergmann, 1962). 



The conditions and type of food which favor the 

 enrichment of the bivalve body with sterols and 

 vitamins are not known. 



Table 45. — Thiamine contents per 100 g. of raw oysters 



from different states 



(From Goldbeck, 1947] 



CONDITION INDEX 



Oysters of good quality have relatively large 

 amounts of meat in relation to their total volume. 

 Their glycogen content is high, and the meat 

 has a creamy color and pleasant flavor. De- 

 termination of glycogen and of the total solids 

 is a time-consuming procedure which cannot be 

 regularly used in the oyster trade. To Caswell 

 Grave (1912) belongs the credit of expressing the 

 quality or fatness of oysters as the percentage 

 of the volume of space enclosed between the two 

 valves occupied by the oyster body. Hopkins 

 (quoted from Higgins, 1938, p. 49-50) developed 

 this idea further and suggested that the ratio 



dry weight of meat in g. X 100 

 volume of cavity in ml. 



is a useful index of quality. Since then the ratio 

 between the dry or wet weight of meat to the 

 volume of the cavity has been used by many 

 investigators in determining the condition index 

 of oysters. The volume of the cavity can be 

 measured by displacement. The oyster shells 

 are thoroughly scrubbed with a wire brush, and 

 each oyster is placed in a glass container provided 



Figure 364. — Glass container used for determining the 

 volumes of whole oysters and oyster shells by 

 displacement. 



with a side arm set at an angle to the side wall of 

 the container (fig. 364). First the zero level of 

 water is marked; then the oyster is introduced, 

 and the level is brought back to zero position by 

 draining the water through a drain pipe at the 

 bottom. The water is collected, and its volume 

 measured. The oysters are then taken from the 

 container, opened carefully, and the meats re- 

 moved. The volume of shells without meat is 

 measured, and the volume of shell cavity is found 

 by the dift'erence between the volume of the whole 

 oyster and the volume of its shell. 



The methods used in determining condition 

 index have not been standardized and, therefore, 

 the values given by different investigators vary. 

 Baird (1958) applied statistical analysis in evaluat- 

 ing the significance of variation of the index. 

 He also demonstrated that little accm'acy is 

 gained by using dry weights as an index measure- 

 ment and that even with fau'ly large samples the 

 fluctuations may be considerable. He concludes 

 that 50 oysters per sample is the largest practicable 

 number. 



392 



FISH AND WILDLIFE SERVICE 



