-27- Conclusions Biological decline of radioactivity in the fishes of Belle Island, Eniwetok Atoll, is generally similar in all species. Differences which are evident may be attributed to differences in feeding habits and, these differences, which appear greatest during the first 100 to 200 days after shot, may be attributed to differences in the uptake and retention of the short-lived isotopes. The decline of the radioactivity in omnivorous fishes is more rapid than that in carnivorous fishes so that 200 days after shot the amount of radioactivity in the two types of fish appears to be quite similar. It might be postulated that omni- vorous fishes ingest food which contains comparatively greater amounts of the shorter-lived isotopes than the food of carnivorous fishes. The decay of radioactivity in the tissues of fish from Belle Island shot, also differs during the first 100 days after the reflecting, to some degree, the unstable ecological condi- tions prevailing in that region at the time. The relationship of the amounts of radioactivity retained in each of the five tissues examined prevails more or less consistently and substantiates findings of previous investigations. The greatest per-gram concentration of radioactive materials occurs in the alimentary tract with the liver, muscle having successively lesser amounts. skin, bone and The greatest vari- ation from this pattern appears during the first few weeks after shot.