Damage Accumulation and Recovery in the Fish Oryzias latipes Exposed to Fractionated or Protracted Radiation at Different Temperatures

Abstract

In the fish Oryzias latipes, 3 to 4 kR of X-irradiation was less lethal if applied in several separate fractions at intervals than if applied in the same total dose given by a single acute exposure. The effect of the dose frac-tionation was clearer if the total time from the 1st irradiation to the last one was longer. In this respect the number of fractions appeared to be of no consequence. Decrease in lethal effect by dose fractionation did not take place if temperature during the interval period was low. A similar dose-fractionation effect was recognized in acute [gamma] -irradiation. Furthermore, in chronic irradiation with a given total dose of [gamma] -rays, the shorter the duration of exposure, the stronger was the noxious effect. However, if temperature during the irradiation was low, the dose-rate effect was not observed. Results support the assumption that recovery from radiation-induced damage proceeds to some extent during the interval between the fractions in acute irradiation, or during "radiation-on time" in chronic irradiation, and that the rate of the recovery is slowed down under low-temperature conditions.