186 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The whole-body Cs'" retention curve of 

 flounder consisted of two rate functions with U^ 

 values of 5.3 and 36.9 days. These are con- 

 siderably lower rates than those found for clams 

 and oysters, both of which had component ij^'s 

 of 3 and 12 days (T. J. Price, unpublished data). 

 It is pointed out that the muscle to organ ratio 

 of fish is large compared to that of clams and 

 oysters, which may account for the longer U^ of 

 Cs"' in flounder. Richmond (1958) expressed 

 the retention of Cs"* in mice, rats, monkeys, 

 dogs, and man as multiple rate function curves. 

 None of the ty^ components for mice or rats 

 exceeded 14 days. The component rate function 

 of monkeys and dogs was more nearly similar to 

 those of flounder, the <^ values being 3, 23, and 

 40.5 days for monkeys and 1.1, 27, and 43.5 

 days for dogs. 



The Cs'^* retention curve for man consisted of 

 two rate functions having ty^ values of 3 and 143 

 days. McNeill and Green (1959) gave the reten- 

 tion of Cs'" in man as a single rate function with 

 an effective half-life of about 115 days. It is 

 likely that the retention curve for flounder might 

 have included a third rate function if it had been 

 possible to continue the experiment. Also it is 

 likely that the long accumulation period prior to 

 the retention experiment might have influenced 

 the characteristics of the retention curve by 

 enabling a greater portion of the Cs'" to be 

 concentrated in muscle. This is suggested by 

 the slow rates of accumulation and loss by croaker 

 muscle as compared to the other tissues. 



Croaker nmscle, with the lowest Cs'" concen- 

 tration at zero time, retained the highest con- 

 centration after 219 days of all tissues tested. 

 This was due to the relatively long /i^'s of 34.8 and 

 94.7 days, botli of which were substantial per- 

 centages (35 and 61 percent) of the Cs"' at zero 

 time. This is significant since muscle represents 

 the greatest mass of tissue. A croaker prepared 

 for the frying pan (less entrails, head, scales, and 

 fins) represents approximately 53 percent of its 

 original body weight; about 5 percent of this is 

 bone, leaving 48 percent edible muscle and skin. 



Liver, in contrast to muscle, had an extremely 

 high Cs"' concentration at zero time, but 61 

 percent of this amount had a t^ of 0.7 day, and 

 37 percent had a <j^ of 4.3 days. Consequently, 

 the concentration was very low at 219 days. 



Although the 911-day ty^ component of gonad 



and the infinite t^ component of liver may seem 

 unusually long, there is no indication that they 

 would have remained unchanged with the arrival 

 of summer temperatures. If observations were 

 begun during the winter instead of the summer, 

 one might expect component rate functions 

 somewhat dift'erent from those obtained. There- 

 fore, the present values should not be interpreted 

 as fixed values, since they might be influenced by 

 changes in temperatm'e, salinity, food availability, 

 and other factors in the environment. 



The authors wish to thank Dr. Earl Denbler, 

 University of North Carolina Institute of Fish- 

 eries Research, Morehead City, N.C., for supply- 

 ing some of the fish used in this investigation, and 

 William S. Davis, for advice on statistical treat- 

 ment of the data. 



SUMMARY 



A series of laboratory experiments were per- 

 formed in which accumulation and retention of 

 cesium^'' by marine fishes were followed. In 

 order to simulate conditions occurring in a marine 

 environment which might control the availability 

 of the radionuchde, Cs^" was administered orally 

 to fish in some experiments while in others the 

 fish were kept in sea water containing known 

 amounts of the radionuclide. 



1. Postlarval summer flounder {Paralichthys 

 dentatus) concentrated 9 to 11 times the amount 

 of Cs'" in sea water during a period of 91 days. 

 The rate of accumulation per unit weight de- 

 creased during periods in which the flounder 

 gained weight rapidly. On the other hand, 

 when the flounder did not significantly gain 

 weight, the rate of accumulation increased. This 

 was attributed to the disparity between rate of 

 accumulation and rate of weight increase. 



2. Atlantic croaker (Micropogon undulatus) 

 concentrated Cs"' in heart, liver, and spleen by 

 a factor of 9 times the amount in sea water after 

 29 days. Muscle accumulated the radionuclide 

 at a slower but more uniform rate with a con- 

 centration factor of 4.5. 



3. Orally administered Cs'" was rapidly ab- 

 sorbed from the digestive tract of croaker with 

 onljr 10.8 percent of the dose remaining after 24 

 hours. 



4. Maximum concentrations of Cs'^' occurred 

 in all tissues of croaker, except muscle, within 24 

 hours following oral administration. 



