Oysters should be taken from a healthy population; 

 they should be devoid of parasites and commensals; 

 they must be of uniform size and age. The 

 metabolism tests should be made at constant 

 temperature and salinity. 



Observations described below were made in 

 accordance with these requirements. Oysters 

 obtained from grounds near the laboratory varied 

 from 9.6 to 10.3 cm. in height and from 6.5 to 

 7.0 cm. in length. They were fully adjusted to the 

 salinity of the laboratory water. The temperature 

 of the water in the respiratory chamber was kept 

 between 24° and 25° C. but changes during each 

 test did not exceed ±0.1° C. The salinity of 

 water was kept constant at the concentration 

 corresponding to the salinity of their natural 

 environment. Tests were performed at Woods 

 Hole and in Milford, Conn.* 



Shell movements were recorded continuously 

 during tests which lasted from .3.5 to 8.5 hours, 

 depending on the behavior of the oyster. If the 

 oysters remained closed for more than 30 minutes 

 the test was discontinued, since it was reasonable 

 to expect on the basis of previous experience that 

 the period of closure would continue for several 

 hours. Samples of water for oxygen determina- 

 tion were taken at half-hour intervals. For the 

 study of seasonal changes of respiratory rates the 

 oysters were marked by engraving a serial number 

 on their left valves. Between tests they were 

 kept in the harbor or in a large outdoor tank with 

 circulating sea water. The data of oxygen uptake 

 are expressed either as cu. ml. of oxygen (at 0° C. 

 and 710 mm. barometric pressure) or as mg. of 

 oxygen consumed per oyster per hour. (To 

 convert the number of ml. into mg. of oxygen the 

 first value should be multiplied by 1.4292.) 



Oxygen uptake of animals is usually expressed 

 per unit of their body weight. In the case of the 

 oyster the use of the total weight may be mis- 

 leading because of the great variations in the 

 weight of metabolically inert shell material. It 

 is, therefore, more sensible to refer to the o.xygen 

 uptake per unit of either wet or dry tissues. The 

 use of dry weight gives more consistant results 

 because in this way the variability caused by 

 changes in the water content of the tissues is 

 eliminated. The rate of oxygen uptake by a 

 single oj^ster of knowni size is, however, of interest 



to ecologists who are concerned with the oxygen 

 requirements of an entire oyster community. 

 Furthermore, in a study of seasonal metabolic 

 changes the experimental oysters could not be 

 sacrificed at the end of each test. Their weight 

 at the end of the entire series of observations 

 would be meaningless because of the changes in 

 solids. The data on seasonal variations in res- 

 piration are, therefore, given in the amounts of 

 oxygen consumed by a single adult oyster in 1 

 hour. 



The range of individual variations in the rate of 

 oxygen uptake by adult oysters of approximately 

 equal size is fairly large. Wide fluctuations fre- 

 quently occur during a single test until the oyster 

 reaches a steady state and remains open with a 

 minimum of shell movement. Therefore, esti- 

 mates of oxygen demand based on one or two 

 readings made shortly after placing the mollusk 

 in the respiratory chamber are meaningless. As 

 the observations described below indicate, the 

 study of the respiratory rates should be based on 

 a series of readings continued for several hours 

 and made at regular intervals. 



Table 23 presents a summary of observations 

 made on 11 adult Long Island Sound oysters, 

 which prior to the tests were kept for at least 4 

 weeks in Woods Hole harbor and were adjusted 

 to the salinity of the laboratory water. With a 

 few exceptions the o.xygen uptake of each oyster 

 remained fairly constant during the test. The 

 mean oxygen consumption per oyster per hour 

 varied from 3.0 to 5.8 mg. The mean value for 

 the entire group was 4.08 mg. of oxygen per hour 

 per oyster. The group apparently divided into 

 two classes of oysters, those with the low 

 metabolic rate of 2.5 and 3.6 mg. of oxygen per 



Table 23. — Oxygen uptake in mg. per hour per oyster of 11 

 adult Massachusetts oysters during 3.5 hours at half hour 

 -intervals at the temperature of 34° to 25° C. 



The tests were made at the Woods Hole laboratory in June before the be- 

 ginning of spawning. Nos. 4, 8, and 11 are females, the others are male. 

 Dimensions of oysters: height 9.6 to 10.3 cm.; length 6.6 to 7.0 cm.] 



' I gratefully acknowledge the valuable cooperation of Walter .\. Chlpman 

 in conducting for me a series of tests at Milford; and to two medical students, 

 now doctors, John F. Reppun and George Mishtowt, who assisted me at 

 Woods Hole. 



Mean of means 4.08. 

 Standard deviation ± 0.337. 



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FISH AND WILDLIFE SERVICE 



