Iron-55 values for thirteen tissues from one skipjack tuna are given in Table 5. April 20 and May 21, This skipjack (M-2) was caught between 1962 in the area 24°-27°N and 157°-160°W. RESULTS AND SUMMARY The amounts of Kio Mn>*, coe? , mn°?, gr? -Nb?>, Ru? and e313? were determined by gamma-spectrum analysis in 1,775 samples. The samples included tissues of light and dark muscle, bone and were obtained from 446 eviscerated fish, swordfish, skin and 438 tuna and 8 caught by Japanese commercial fishermen in the westerr. Pacific between February 20 and October 19, 1962. were grouped into six periods, May to October, The samples corresponding approximately to the month in which the fish were landed in Tokyo. From these analyses, l. the following observations have been made: The radionuclide values were small; many values--80 per cent of the fallout radionuclide values--were not significantly greater than the background counts. 2. The average vaiues by month of landing and by tissve for naturally-occurring KO in terms of picocuries per gram of wet tissue {pc/g wet) ranged from 0.6 (bone, August} to 5.2 {dark muscle,May ). 3. The average values by month of ianding and by tissue for the six fallout radionuclides were less, much iess, tha- the K values in all and usually very except seven of 168

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