- 3- are a means by which radioisotopes are transferred from the sea to man and the transfer results in a hazard to man's health, this is also an effect upon our welfare. Of the two effects, the role of fish in transfer- ring radioisotopes from the sea to man is of greater con- cern than the mortality that may occur to the fish. ever the contamination is in the sea, What- the transfer of radioisotopes from the sea to man will be of some concern, whereas the loss of fish would occur and be of concern only under unusual conditions of very great contamination. The condition that is most likely to be expected in the sea is that in which fish may acquire some radioisotope in an amount that is not lethal to the fish but when taken up by man by eating fish possibly could be concentrated to a2 level that is above the maximum permissible amount for man. Another reason that the indirect effect upon man is more important than the direct effect upon fish is that under conditions of equally heavy contamination of land and sea, man would succumb to radiation before fish, and therefore the mortality to fish would come too late to be of concern. Fish are less sensitive to external ionizing radiations than man, the lethal dose being about twice as great for