~ 53 radioisotopes in other plankton samples collected one to six weeks post shot, with fallout from more than one deton- ation, are given in Table V. In the two tables only those radioisotopes that were present in the amount of about one per cent or more of the total activity are listed. Undoubt- edly other radioisotopes were present but the greater abundance of the isotopes listed overshadows the isotopes present in minute quantities. Other information about radioisotopes in sea water is included in the discussion that follows on the uptake of radioisotopes by fish. UPTAKE OF RADIOISOTOPES BY FISH In the discussion ot the uptake of radioisotopes by fish, principal consideration will be given to the isotopes that are most likely to be transferred to man. Maximum transfer from sea to man requires that the radioisotopes are in an available form and are elements of nutrition for fish and water, man. In Table IV certain elements present in sea sea foods and fish muscle and the concentration of the elements in fish muscle are given. The elements selected for Table IV as being most likely to be transferred to man are the essential mineral