water transport 



jjd^JMjimM^ 



shell movement 



-L 



_L 



X 



Figure 181. — The shell movements and rate of water transport of an adult C. virginica preceding the closing (leftside) 

 and following the opening (right side) of the valves. Temperature of water 22.5° C. Time interval 1 hour. 



the difficulty by assuming that "each oyster ap- 

 pears to have a threshold limit to the carbohydrate 

 below which it will not pump." 



The existence of a general chemical factor which 

 controls the principal activity of the oyster would 

 be of great importance to the study of feeding and 

 nutrition of marine invertebrates. It seems that 

 if such a factor actually exists then Putter's 

 theory of the significance of dissolved organic 

 substances in the feeding of marine invertebrates 

 should be reinvestigated, especially in view of the 

 assertion made by Collier and his colleagues that 

 "the oysters remove variable quantities (up to 

 50 mg./l.hr.) of the carbohydrates from sea water." 



a 4 

 o 3 



50 75 100 25 



75 200 25 50 75 300 25 50 75 400 25 

 SECONDS 



Figure 182. — Effects of egg .suspension on the water 

 transport by the lateral cilia of the gill of a ripe male 

 oyster, C. virginica. Data from the drop counting record 

 are plotted as averages of 5 sec. intervals. Temperature 

 of water 22.5° C. 



An attempt to identify the substances concerned 

 was made by Wangersky (1952), who reported 

 the isolation of a compound having the absorption 

 spectrum of dehydroascorbic acid and the presence 

 of a substance which "gives some indication of 

 rhamnoside" and is found in the inshore waters 

 of the Gulf of Mexico in concentrations up to 



0.1 g./l. 



A description of the reagents and methods for 

 carbohydrate determination can be found in the 

 paper of Lewis and Rakestraw (1955) who remark 

 that in general, the N-ethyl-carbazole method 

 (used by Collier, Ray, Magnitzky, and Bell) is 

 "considerably less satisfactory" than the anthrone 

 method. 



The N-ethyl-carbazole method is as follows: 1 g. 

 of the reagent recrystallized from ethanol and 

 water is dissolved in one liter of 90 percent sulfuric 

 acid cooled in ice. The acid should be of highest 

 purity, stored in glass-stoppered bottles. The so- 

 lution is stored in a dark bottle and kept refriger- 

 ated. Exposure to air and sunlight must be 

 avoided as much as possible. Under these condi- 

 tions the reagent is stable for at least 2 days. 



A 2.5-ml. sample of filtered (or centrifuged) sea 

 water is transferred to a 60-ml. bottle, 22.5 ml. of 

 N-ethyl-carbazole reagent is added, and the sample 

 thoroughly mixed. The sample is immediately 

 placed in a water bath at 70° C. ( ± 0.2° C.) and 

 left for exactly 30 minutes. After 15 to 20 min- 

 utes in a refrigerator the sample is allowed to come 

 to room temperature. The optical density at 562 

 mix is determined between 30 to 60 minutes after 

 the removal of the sample from the water bath. 



198 



FISH AND WILDLIFE SERVICE 



