176 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



an increased carbohydrate concentration because 

 of increased temperature, the oyster recorded in 

 the lower figure went from phase II into phase 

 III at interval E, following four unfavorable 

 testing periods A through D. 



The association of increased pumping rate with 

 a threshold level of carbohydrate concentration 

 and the effect of increasing temperatures on this 

 threshold level are obvious. 



Having demonstrated the instantaneous pump- 

 ing-rate response of the oyster to changing con- 

 centrations of carbohydrates, we examined the 

 records of cumulative hourly pumping-rate 

 responses to these changes. Figure 8 showing on 

 a semilog scale the reaction of a typical oyster 

 (No. 92), and of five oysters combined, to the 



changes in carbohydrate concentration, makes it 

 evident that despite the stated limitations of this 

 method to measuring the carbohydrate activity 

 ratio, the relative changes in hourly effluents do 

 parallel very closely the relative changes in 

 carbohydrate concentrations. The low effluent 

 rate preceding 18 b 00 m on January 27 is coincident 

 with phase-II pumping, and occurs with the 

 carbohydrate concentrations below the threshold 

 level for that temperature. With the rise in 

 carbohydrate concentration above the threshold, 

 the pumping rate increases to that of phase III. 



Figure 9 illustrates, on a semilog scale, the 

 relation of the average-cumulative-daily effluent 

 to average-daily level of carbohydrate concentra- 

 tion, based on records of two to four oysters 



e 



-j i i_ 



12 



i i 



IE 20 

 -■- ' I I I I 1_ 



O 



-I I 1_ 



12 



_1 1_ 



16 

 ■J I I I I 



jJJ: Approximote limit ot Phosell pumping (litres per hour) 



e 12 16 20 4 e 12 IS 20 



JANUARY 27 JANUARY 28 



Figure 8. — The relation between carbohydrates and cumulative-hourly effluents over a 2-day period, plotted on semilog 



scale. The curve for an individual oyster is shown, together with the average values for all the oysters being recorded 



during the same period. In each case the hourly effluent went above the phase-II level when the carbohydrates 



went above 4 mg./l. During the twentieth hour of January 28, an external factor interfered. The oysters responded, 



but had begun to recover at the close of the period 



