observed. Although it is recognized that observations of dying fish may not be apparent because of the removal by predators of fish in a weakened condition, it is believed that the amount of radioactivity in water necessary to kill fish directly would have to be greater than the amount of radioactivity that has occurred in the water in the vicinity of Bikini-Eniwetok. If fish survive exposure to ionizing radiations there still may be non-lethal effects in the form of pathological or genetic damage from either external or internal emitters. Again referring to the Bikini-Eniwetok area, thousands of fish have been examined for gross pathological and morphological changes but no obvious changes have been observed (Welander 1959). However, Gorbman and James (1959) found upon examining microscopically the thyroids of reef fish from an area close to a test site that the damage to the thyroid ranged from zero to 100 per cent. thyroid was damaged, In those fish in which the the fish upon superficial examination otherwise appeared to be normal. The cause of damage to the thyroids was undoubtedly radioisotopes of iodine, emitters, as internal that are present in relatively great abundance immedi- ately after the detonation of a nuclear device. As the half life