~23-
and water were analyzed for radioactivity.
Of these, more
than 500 showed some potassium-40 activity.
The levels of
radioactivity of potassium-40 averaged 3.4 and 2.8 pc/g of
wet tissue for dark muscle of yellowfin and bigeye tuna, respectively.
The levels in other species were similar, but the
ranges indicate considerable variation in each.
The level in
light muscle of both yellowfin and bigeye tuna was 3.9 pc/g of
wet tissue.
These values are almost twice as great as the
values determined for similar tissues and species of fish by
Chakravarti and Joyner
(1960).
They obtained values of 1.89
and 1.92 pc/g of wet weight for dark and light muscle,
respec-
tively; the values were based on the amount of stable potassium
as determined by flame spectrophotometry.
Flame spectrophotometry analyses of 10 samples of mixed
light and dark muscle of yellowfin tuna, with an average po-
tassium-40 count of 3.48 pc/g wet weight,
resulted in a count
of 2.73 pc/g as calculated from the amount of stable potassium
present.
It would appear that these levels of activity of po-
tassium-40 are high,
and also that there is a great deal of
variation in the potassium content in fish muscle.
SUMMARY AND CONCLUSIONS
Four oceanic surveys within 600 miles of Christmas Island
were made,
March through August,
1962,
prior to,
during and