174 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



definite characteristics of flow through the bran- 

 chial system (here we arbitrarily include the 

 promyal passage). Phase I may permit a slight 

 flow or none, at all; phase II involves some flow, 

 although much less than does phase III. The rela- 

 tion between these phases and their respective 

 pumping rates are typified in figure 5, which is a 

 reproduction of an actual record showing rates 

 of pumping in each of the three phases. 



EFFECT OF CARBOHYDRATES ON 

 PUMPING RATE 



In these experiments the carbohydrate concen- 

 tration in the laboratory sea-water supply varied 

 widely. Variations over the entire range within a 

 few hours were common; often variations were 

 100 percent within 2 hours. Such extreme varia- 

 tion precluded the use of averages in analyzing the 

 data relating carbohydrate concentration to pump- 

 ing rate. 



The hourly effluents, therefore, were computed 

 from pumping rates measured at the time the 

 carbohydrate concentrations were measured. 

 Samples for these carbohydrate determinations 

 were taken from the inhalant side of the oyster, 



not from the sampling wheel (see Appendix, p. 183), 

 which was located at some distance from the 

 oyster. Over a long period of time using a number 

 of oysters, we have found a positive correlation 

 between the carbohydrate concentration and the 

 pumping rate of the oyster, as shown in figure 6. 

 An interesting phenomenon, observed in the 

 detailed study of the oyster's response to carbo- 

 hydrates, is the testing period, illustrated in 

 figure 7. Variation of the carbohydrate con- 

 centration at a temperature of approximately 25° 

 C. is illustrated in the upper figure. Until 

 10 h 00 m , the carbohydrate concentration was about 

 6 mg./l., followed by a rise within 2 hours to the 

 10 mg./l. level. At the beginning of the interval 

 marked A the valves opened into phase II, during 

 which period a small amount of water was passed 

 through the oyster. At this temperature the 

 carbohydrate level was too low to stimulate the 

 oyster to further activity. After a short period 

 of closure, another test was made at interval B. 

 Within 30 minutes, the concentration of carbo- 

 hydrates having risen while the valves were still 

 in phase II, progress into phase III was induced 

 as shown in intervals C and D. Similarly, but at 



o 

 O 



0800 



0900 



1000 



1100 



Time 



1300 



1400 



1200 



of day 



Figure 6. — Relation between pumping rates and carbohydrate concentrations. The pumping rates were determined at 

 the moment the carbohydrate samples were taken. The mean carbohydrate concentration is 13.4, and the mean 

 pumping rate 9.15 liters per hour. The correlation coefficient, 0.78, is significant at the 1-percent level. 



