178 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



34-204 grams; bluefish, Pomatomus saltatrix 

 (Linnaeus), 250-350 grams and little tuna, 

 Euthynnus alleteratus (Rafinesque), 5.4-6.1 kilo- 

 grams. Fish were weighed immediately prior to 

 radioactivity measurements. Flounder were kept 

 in small indoor tanks and fed nauplii of the brine 

 shrimp, Artemia salina. Croaker, bluefish, and 

 little tuna were kept in large outdoor tanks and 

 all except little tuna were fed cut fish. The 

 latter would not accept food while in captivity, 

 and the only experiment utilizing this species was 

 limited to 8 days. 



The carrier-free Cs'" used in the present ex- 

 periments was obtained in the form of CsCl in 

 0.12N HCl from the Oak Ridge National 

 Laboratory, Oak Ridge, Tenn. It has a half-life 

 of 30 ± 3 years and is in secular equilibrium with 

 Ba'", which has a half-life of 2.6 minutes. 



EXPERIMENTAL PROCEDURE 



Fish accumulate radioactive Cs by direct 

 absorption from the water and by ingestion of 

 food and water. Both pathway's were followed 

 in the present experiments. Radioactivity ab- 



sorbed by tissues of fish kept in standing sea 

 water containing a given concentration of Cs'^" 

 was measured (radioassayed) periodically. To 

 determine the amount of absorption from the 

 digestive tract, Cs'" was administered orally to 

 fish which were kept in flowing sea water and 

 radioassayed periodically. 



Accumulation by absorption from sea water 

 was followed in flounder and croaker. The water 

 was first filtered through cotton to remove 

 particles which might take up Cs'". Frequent 

 radioassay and renewal of the water insured a 

 minimum variation of the Cs'" content and pre- 

 vented a buildup of excretory products. The 

 water was aerated and had an average salinity of 

 32±3°/oo. Twenty-nine flounder were kept in 

 a battery jar containing 5 liters of sea water with 

 a Cs'" concentration of 0.1 ^c per ml. The jar 

 was placed in a bath of flowing sea water to 

 maintain a temperature within the range of that 

 in the natural environment. During the experi- 

 ment the temperature gradually increased from 

 8° to 18° C. Twenty-four croaker were kept in 

 a tank containing 48 liters of sea water with 



Figure 1. — Accumulation of Cs'" by postlarval flounder from sea water as influenced by growth rate. Upper curve 

 is based on the ratio of radioactivity in fish to that in an equal weight of water. Center curve is based on radio- 

 activity per individual. Lower curve represents mean weight of fish. Vertical lines are one standard deviation 

 above and below curve. 



