pended material and accumulation of metabolites. 

 The methods are not suitable for continuous ob- 

 servations since they should be completed in the 

 relatively short time before tmbidity of the water 

 is changed because of the aggi-egation and floccula- 

 tion of suspended particles. Finally, computa- 

 tion by turbidity observations of the volume of 

 water filtered by mollusks is based on the assump- 

 tion that mechanical precipitation, due to gravity, 

 remains constant. This, however, is not the case. 

 J0rgensen and Goldberg (1953) found that C. vir- 

 ginica removes graphite particles from 5 to 10 

 times faster from a 4-hom" old suspension than 

 from a fresh one. This effect is explained by the 

 difference in the size of the particles which in the 

 aged suspension are about 2 to 3 /j in diameter; 

 in the fresh one they are less than 2 ;u. By adding 

 small amounts of carmine suspension to the gill of 

 the oyster it is easy to notice that the filtering 

 efficiency of the gills of C. virginica and C. gigas 

 is not high and that many small particles appear 

 in the cloacal cui'rent. J0rgensen (1943) assumed 

 that all particles are removed as the water is 

 filtered through the gills, and computed the rate 

 of water transport m by using the following 

 formula: 



m- 



(log conco— log cone,) M 

 log e  t 



where m is the volume of water (in liters) trans- 

 ported in 1 hour; M is the volume of suspension in 

 liters; conCo and conct are the concentrations of 

 cells or particles at the beginning of the observa- 

 tions and after t hours ; and e is the Napierian base 

 (2.71828). The formula can not be expected to 

 give accurate results because it is based on two 

 incorrect assumptions: fu-st, that all suspended 

 particles are removed from the water as it is being 

 transported through the gills; second, that the dis- 

 persion of particles in the suspension does not 

 change dming the duration of the test. J0rgen- 

 sen's observations showed considerable differences 

 in the properties of new and old suspensions of 

 graphite, and Chipman and Hopkins (1954) demon- 

 strated that the efficiency of the removal of cells 

 changes with time and is not related to cell concen- 

 trations. In their experiments the rapid rate of 

 removal of Nitzschia or Chlamydomonas cells was 

 followed by a decrease in the filtering efficiency of 

 the gills and in the increased retm-n to the suspen- 

 sion of the phytoplankton cells which had passed 

 through the gills. 



These difficulties introduce great uncertainty in 

 the studies of the rate of water transport by the 

 gills based on turbidity determinations. Some of 

 the problems may be solved by the use of radio- 

 active plankton. 



Use of radioactive plankton. — The advance of 

 radioisotope techniques has made it possible to 

 employ labeled plankton algae for determining 

 their rate of removal by water-filtering mollusks. 

 Chipman and Hopkins (1954) and Chipman (1959) 

 applied this method in a study of the rate of water 

 transport in bay scallops, and Smith (1958) ex- 

 tended their observations to the clam, Mercenaria 

 (Venus) mercenaria. Single species cultures of the 

 diatom Nitzschia closterium (56 m in length) and a 

 species of Chlamydomonas (7^ in size) were made 

 radioactive by the incorporation of phosphorus, 

 P^-. The cells grown in a culture medium (modi- 

 fied Aliquel solution) that contained virtually no 

 phosphorus except the P^^, were highly radio- 

 active. This isotope, emitting only beta particles 

 of rather high energy, was found to be useful for 

 this purpose. The details of the method de- 

 veloped in the Biological Laboratory of the Bureau 

 of Commercial Fisheries at Beaufort, N.C., are 

 described in a paper by Rice (1953). The method 

 is extraordinarily sensitive and allows detection 

 of very slight changes in cell numbers which other- 

 wise would have remained unnoticed. The use of 

 radioactive plankton presents several advantages 

 in studies of the functions of the gills; it allows 

 observations without undue increases in the con- 

 centration of suspended material and it makes 

 possible recordings of changes in the rate of water 

 transport which could not be detected with other 

 methods. 



CONTROL OF RATE OF WATER TRANSPORT 

 THROUGH THE GILLS 



Estimates of the rate of water transport by an 

 adult oyster, made by investigators who have 

 studied the problem carefully, vary from several 

 liters to a maximum of 34 l./hr. (Loosanoff and 

 Xomejko, 1946). Naturally the rate of water 

 transport depends on the size of the oyster, its 

 physiological state, and environment. The abso- 

 lute figures are, therefore, of little significance 

 unless they are accompanied by data on tempera- 

 ture, conditions under which the tests were made, 

 and size of the oysters used. 



It is self-evident that the quantity of water 

 propelled by the gills must depend on the size of 

 the mollusk. No comparative data of this 



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FISH AND WILDLIFE SERVICE 



