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distribution of radioactive materials was evidently still in a state of considerable flux eight
days after the shot. Surface contamination or the presence of radioactive material in the contents of the digestive tract accounted for most of the radioactivity found in the invertebrates.
An appreciable amount, however, was absorbed into the tissues. Muscle consistently had the
lowest specific activity, and digestive tract, with its contents, the highest. Other tissues or
~
organs varied in rank, depending on the species. In general, invertebrates taken at the northern
stations were the most radioactive. The decrease in radioactivity from north to south appeared
to be more rapid on the east than on the west side of the lagoon.
4.5 FISH
4.5.1
Materials and Methods
The fish specimens were collected in water poisoned with derris-root powder in depths
to 12 {t, usually on the lagoon side of each of the station islands. Areas selected for poisoning
had a minimum of current aa well as adequate coral and substrate to support the typical reef
population of fish.
The numberof fish collected varied from 26 to over 300 per station, depending on the
success of the poisoning operation and the number of species present. These fish represented
from 10 to more than 30 families and varied in weight from less than 1 to 1589 g (average
51.1 g).
Although there were several hundred species of fish living on the reef, the species selected
for analysis of radioactivity were those most commontoall stations and those that were representative of the various types of feeding habits. Most of the species selected were reef
dwellers and more or less sedentary; however, a few, such as goatfish, jacks, and flatfish,
which prefer an open sandy bottom were also taken and ashed for counting.
The fish which best fulfilled the criteria listed above were the damselfish (Pomacentridae),
surgeonfish (Acanthuridae), grouper (Serranidae), and wrasse (Labridae), Table C.3, which
summarizes the material used in the analysis for radioactivity, shows that these four families
were taken at all stations. Certain species, such as the grouper, Epinephelus merra, the
damselfish, Abudefduf biocellatus, the surgeonfish, Acanthurus triostegus, and the wrasse,
Halichoeres trimaculatus, were taken at a majority of the stations.
n
A total of 237 specimens representing 58 species, 33 genera, and 22 families of fish
were counted for radioactivity on 768 plates.
The following organs of the large specimens selected were analyzed for radioactivity:
muscle, skin, bone, liver, and gut (including contents). In smali fish the following were combined for analysis: (1) muscle, skin, and bone; (2) gut and liver; or (3) entire fish. Omnivores
and carnivores were selected in approximately equal numbers at each station.
,
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In order to compare the activity found in various samples of entire fish, the total activity
per gram of an individual fish was calculated as the sum of the activity of all tissues, the
procedure! followed in 1949. The results are recorded in Table 4.10. The tissues listed in
this table made up at least 95 per cent of the total weight of the fish. Gills, glands, and nervous
tissue were assumed to be simiiarin activity to bone, skin, and muscle.
4.5.2 Analysis by Area
Comparisons of averages for entire fish indicate that the greatest amount of radioactivity
was in postshiut samples collected at Engebi Island, followed by Fogallua, Aaraanbiru, Rigili,
Runit, Igurin, and Japtan in descending order (Table 4.10 and Fig. 4.2).
If the tissues are analyzed by stations, a slightly different order is indicated. Activity in
To?
.
oe
.
muscle is greatest at Bogal.ua, followed by Engebi, Aaraanbiru, Rigili, Igurin, Japtan, and
Runit. The sequence is similar for the activity in bone, skin, and liver, except for a shifting in
the last four islands. Japtan generally appears to be lowestin activity, with Igurin next lowest,
38