-12- radioactive isotopes of cobalt account for 7 to 20 percent of the radioactivity and Mn>4 2 to6 percent. The minimum concentrations of radioactive materials are found in the carnivores, for these fishes, like the reef-dwelling groupers, or the roaming carnivores, like the tuna and barracuda, obtain their "tag" of radioactive material only after it has been passed through a number of living forms which select, retain, or reject various radioisotopes. With the passage of time longer-term studies indi- cate that several years after a single contamination of an area the carnivorous fish contain the greatest amount of radioactivity. The carnivorous fish such as tuna and bonito, caught in the Open ocean, contain Zn§5 at the highest levels of any of the three groups of fish. In these animals Zn6° accounts for 75 to 92 percent of the total radioactivity; Fe99-59 | 6 to 25 oercent; the cobalt radioisotopes,1 to 3 percent, and Mn°4 , less than 1 percent. In ‘all species of fish, the greatest amountof radioactivity is found in the alimentary tract, with liver, skin, bone and muscle having lesser amounts in descending order. Skin and bone are quite similar in the amounts present, and usually the radioactivity averages twice that found in the muscle. about The liver may have two to nine times as much radioactivity as the bone or skin, and the alimentary tract contains two to four times as much as the liver.