cesium'" in marine fishes 



179 



a Cs'" concentration of 0.0005 nc per ml. and 

 a temperature of 21±1° C 



The method selected for administering Cs'^" 

 orally was that most easily adapted to the par- 

 ticular species of fish. When croaker were used, 

 the radionuclide was pipetted directly into the 

 stomach. However, bluefish regurgitated the 

 liquid, so each dose was changed to a solid by 

 the following method: One-tenth ml. of the 

 radionuclide was pipetted on a small piece of 

 aluminum foil. Into this droplet powdered 

 gelatin was sprinkled until it appeared dr}' on 

 the surface. The foil was placed on a hotplate 

 set at low heat until the preparation became clear. 

 It was then removed from the hotplate, allowed 

 to dry for about 4 hours and the dose was peeled 

 from the foil and rolled into a cylinder. After 

 drjdng overnight the dose became quite hard and 

 was introduced into the esophagus of a bluefish 

 by the use of forceps. Because of the extremely 

 large mouth and throat of little tuna, the gelatin 

 doses were first inserted into the body cavity of 

 the pinfish, which in turn were fed to the little 

 tuna bj' the use of forceps. The amount of Cs"' 

 given varied from 0.4 to 1.0 /ic per gram of fish. 

 Since the Cs'^' administered to fish was greatly 

 diluted from the acid stock solution and the 

 volume of each dose was only 0.1 ml., the pH of 

 the contents of the fish stomachs was not 

 significantly affected. 



In measuring the Cs'" content of postlarval 

 flounder, each fish was rinsed in a screw-cap vial 

 containing 2 ml. of nonradioactive sea water, 

 weighed, and radioassayed alive. By following 

 this procedure it was possible to radioassay all of 

 the flounder at each time interval. 



Measurements of radioactivity in croaker or 

 bluefish were averaged from four or five indi- 

 viduals per time interval, but only one little tuna 

 was measured because of the difficulty in keeping 

 a sufficient number alive. After careful dissec- 

 tion, small portions of certain tissues were excised 

 from the same relative positions in all fish. These 

 were placed in screw-cap vials, weighed on a preci- 

 sion balance and radioassayed. Blood samples 

 were taken from the truncus arteriosus with a 

 hypodermic syringe after first making an incision 

 to expose the heart. In some instances both blood 

 serum and whole blood were measured. Separa- 

 tion of the cells from the serum was accomplished 

 by centrifuging the coagulated blood. 



RADIOASSAY OF TISSUES 



Gamma ray emission of tissues was measured 

 with a well-type scintillation crystal in which 

 0.01 lie of Cs'" yielded a rate of 6,500 counts per 

 minute. Counting rates were not influenced by 

 biological separation of Cs'" and Ba'^' since the 

 short half-Ufe of Ba'" permitted the return of 

 secular equilibrium before the samples were radio- 

 assayed. All measurements were of required 

 duration to insure a maximum standard devia- 

 tion of 2 percent. Decaj^ corrections were applied 

 only when experiments exceeded 90 days. In 

 accumulation experiments measurements of Cs'^' 

 are expressed either in counts per minute per unit 

 weight of tissue, or as a concentration factor, the 

 ratio of radioactivity in fish tissue to the radio- 

 activity in sea water on a imit weight basis. 

 When Cs''^ was administered orall}', all fish of a 

 group were given the same quantity, and measui-e- 

 nients of radioactivitj'' in the tissues were corrected 

 to a fish of standard weight. In retention experi- 

 ments, measurements are expressed as percentages 

 of the radioactivity present at zero time. All 

 values are presented as averages. 



RESULTS 



ACCUMULATION 



Accumulation of a radioactive substance by 

 an organism occurs when the rate of uptake 

 exceeds the rate of excretion. As stated previ- 

 ously, fish in the marine en\'ironment maj" ac- 

 cumulate Cs"' directly from sea water or from 

 ingested food. Absorption tlu-ough both path- 

 ways may occui" either simultaneously or at dif- 

 ferent times, depending on the food habits or 

 migratory patterns of the fish concerned. In the 

 present experiments, absorption was followed 

 through the two pathways independently so 

 comparisons could be made between them. 



Accumulation from sea water 



WTaole-body accumulation of Cs'" from sea 

 water by postlarval flounder was followed during 

 a period of 91 days. The experiment was begun 

 with 29 fish, but the number was reduced to 24 

 by mortality during the first 14 days. One addi- 

 tional fish died during the remaining 77 days. 

 The rate of accumulation was fairly uniform 

 dui-ing the first 30 days (fig. 1). From the 30th 

 to the 50th day the rate leveled oft' at a concentra- 

 tion factor of 9, accompanied by a slight increase 



