8.0 7.5 7.0 6.5 6.0 



pH OF SEA WATER 



5.5 



Figure 195. — Effect of lowered pH on the rate of oxygen 

 uptake of adult oysters. Summary of summer ex- 

 periments at Woods Hole at 25° C. 



RESPIRATORY QUOTIENT, R.Q. 



The respiratory quotient (R.Q.) is the ratio of 

 the volume of carbon dioxide produced to the 

 volume of oxygen consumed at the same time. 

 Definite values of R.Q. have been recognized for 

 the principal types of food (Vernon, 1895; Richard- 

 son, 1929; Krogh, 1941). The R.Q. for carbo- 

 hydrate is 1.00; for protein abotit 0.79; and for fat 

 0.71. On an average mixed diet the R.Q. of man 

 is about 0.80 to 0.85. The herbivorous animals 

 tend to have a higher R.Q., while the carnivorous 

 have a lower one. 



2 3 4 5 



HOURS AFTER START 



Figure 196. — O.x^'gen uptake of two oysters of approxi- 

 mately equal size (about 6 cm. in lieight) at pH 8.1 

 and 5.8. Salinity 31.6 °/oo. Measured for 6'^ con- 

 secutive hours. Temperature 24.5° C. 



212 



It is of interest to find out whether the R.Q. of 

 the oyster, which is an herbivorous mollusk, 

 changes after the breeding season when it begins 

 to acctimulate and store glycogen. Orton (1927a, 

 1927b) suggested, without presenting supporting 

 evidence, that during the reproductive cycle of 

 O. edulis there is a shift from predominantly 

 protein to carbohydrate metabolism and that this 

 shift is correlated with the completion of the male 

 sexual phase. 



In conducting observations on carbon dioxide 

 production it is necessary to keep in mind that 

 deposits of calcium carbonate in the bodies of 

 some marine invertebrates may suddenly release 

 large quantities of this gas which would give a 

 false R.Q. (Bosworth, O'Brien, and Amberson, 

 1936). For instance, the reported R.Q. 1.39 of 

 lobster was found to be false since in lobsters 

 coated with collodion the R.Q. was only 0.92. 

 The shell of the bivalves is the principal storage 

 place of carbonates which act as buffers when the 

 valves are closed. In metabolism studies this 

 possible soiu-ce of error should be eliminated by 

 coating the shells with paraffin. 



The values of respiratory quotients vary during 

 the conversion of food substances witliin the 

 organism. Fattening of livestock and birds by 

 forced carbohydrate feeding is usually accompanied 

 by high R.Q., while the utilization of fats and 

 proteins and their possible conversion to carbo- 

 hydrates lowers the R.Q. values. It is, therefore, 

 possible to expect that seasonal variations in the 

 R.Q. of the oyster would give a clue to changes in 

 the titilization of its food. 



A Van Slyke constant volume apparatus for 

 gas analysis was used in a series of observations of 

 a group of marked oysters kept in live boxes in the 

 liarbor. Xo definite trend in the changes of R.Q. 

 could be detected. It varied throughout the year 

 from 0.51 to 1.44 as may be seen in the summary 

 of observations (table 28) made under standard 

 conditions in water containing no plankton. 

 Addition of water soluble food in the form of 

 dextrose resulted in an increase in R.Q. The 

 latter determinations (table 29) were made in 

 filtered water to which dextrose was added. 

 There was no increase in R.Q. in water containing 

 0.0025 percent dextrose, but in 0.005 and 0.01 

 percent the R.Q. \alues were significantly higher. 



RESPIRATION IN OTHER SPECIES OF OYSTERS 



Comparison between the results described for 

 C. liryinica and the data published by others for 



FISH AND WILDLIFE SERVICE 



