55 The frequency distribution of the specific activity of ~ Fe in tuna caught north of the equator and of tuna caught scuth of the equator in 1967 and 1968, single school, and in tuna, presumably from a caught at approximately 11°N in dune 1969 are. shown in Figure 1. The distributions have a strong positive skewness, With a definite tendency for a greater proportion of higher specific activities in tuna caught north of the equator. The tuna presumed to be from a single school off Bikini Atoll show a Similar frequency distribution, although the range of specific activity values was less than in the other groups. Attempts were made to correlate various parameters such as species, 55 Fe tf month of catch, . i lecation of tos concentrations or specific catch, a ae activities; and size of fish with however, . toes no signifi- cant relationships were found other than the tendency for fish . - caught north of the equator to have higher concentrations of 55 Fe and higher specific activities than fish caught south of the equator. - 1. 29 Values at the extremes of the ranges for both Fe con- centration and specific activity, were found in tuna caught near the equator, 8°N for example, and in tuna caught at 39°N. . x 55 . tes Results of comparisons made of the Fe content and specific activities of the light muscle, dark muscle, and liver from the sixteen yellowfin tuna cavght off Bikini are given in Table 1. Log 55 Lice ates . c Clearly, determination of Fe specific activity in any of the wre gar ARO