Table 21. — Rate of water transport, in liters per hour, of 

 three adult C. virginica in natural sea water and in xoater 

 containing 1-arabinose in the concentrations of 65 mg., 

 80 mg., and 100 mg./l. Salinity 31.2 "/co 



[In all three experiments the shift from natural sea water to arabinose solution 

 in sea water and again to sea water was made at the end of tlie hour shown 

 in the first column without disturbing the oyster. Fifteen minutes were 

 needed to fiush the experimental tank with natural sea water.] 



In another test using an oyster with a h)\ver 

 rate of water transport the results were as follows: 



Before adding arabinose 3.9 l./hr. during 2 hours 



After addition of arabinose (85 mg./l.) 



4.3 to 4.6 l./hr. during 2 hours 

 Return to natural sea water 



5.6 to 6.0 l./hr. during 2 hours 



During both tests the salinity of the water was 

 .31.2 °/oo and the temperature varied between 

 18.0° and 19.5° C. In the concentration of 102 

 mg./l. of fructose the following rates were 

 observed: 



Before adding fructose 



3.9 to 4.1 l./hr. during 2 hours 



In fructose solution 2.8 to 4.7 l./hr. during 3 hours 



Return to natural sea water 



4.3 to 4.5 l./hr. during 2 hours 



No effects were observed even when the con- 

 centrations of carbohydrates were increased to 

 0.5 percent. The rate of water transport in 

 natural sea water varied between 8.4 and 10.8 

 l./hr. and from 7.2 to 10.8 in the arabinose solu- 

 tions. Similar negative results were obtained in 

 1 percent maltose and 1 . percent fructose in sea 

 water and in various concentrations of ascorbic 

 acid. 



Additional tests with ascorbic acid were made 

 with the carmine cone method for measuring the 

 velocity of the cloacal current. The results 

 (table 22) show lack of any effect on tlie efficiency 

 of the lateral cilia in concentrations var\-ing from 

 10 to 50 mg./l. Velocity of the cloacal current is 



given in table 22 as an average of 10 consecutive 

 i-eadings made at 2-minute intervals. Fifteen 

 minutes elapsed between each group of 10 readings. 

 The concentration of 400 mg./l. (0.04 percent) 

 completely inhibited the current. 



My observations are in full agreement with the 

 results obtained by Butler and Wilson (1959), 

 who presented conclusive evidence that the 

 increases and decreases in the rate of water trans- 

 port by oysters (C virginica) at the Bureau's 

 Biological Laboratory at Gulf Breeze, Fla., (the 

 place where CoUier's experiments were conducted), 

 are not correlated with the changes in the con- 

 centrations of carbohydrates in the water and that 

 there is no "minimal threshold level of carbo- 

 hydrate concentration below which oysters fail 

 to pump." 



The experimental studies show that the organic 

 substances which give an N-ethyl-carbazole reac- 

 tion have no effect on the water transport of oysters 

 in the concentrations in which these substances 

 are encountered in the tidal waters of Cape Cod. 



RESPIRATION 



Exchange of gases takes place primarily in the 

 gills, but the mantle also has a role of lesser 

 importance in the respiration of bivalves. Obser- 

 vations on the comparative rate of oxygen con- 

 sumption by various tissues of the oyster have not 

 been made, but the data on oxj'gen consumption 

 by the gills and mantle of the hard clam Mer- 

 cenaria (Venus) mercenaria are available. Hop- 

 kins (1946) compared the oxygen consumption of 

 the mantle of that species with that of the gills 

 and found that the oxygen uptake by the gills 

 varied from 815 to 912 and that of the mantle 

 only from 11.73 to 15.52 cu. mm./hr./g. of dry 



T.4BLE 22. — Effect of ascorbic acid on the velocity of cloacal 

 current of C. virginica 



(Carmine cone method. Temperature 19.6° to 20.6° C. Each figure of 

 velocity is an average of a group of 10 consecutive readings. Time inter- 

 val between each group— 15 minutes.] 



200 



FISH AND WILDLIFE SERVICE 



