Effects of Low-Level Chronic Irradiation of Chinook and Coho Salmon Eggs and Alevins

Abstract Chinook and coho salmon eggs were subjected to about 0.5 roentgen per day of the gamma radiation from cobalt-60 from shortly after fertilization until the alevins swam, resulting in a total dose to the chinooks of from 33 to 37 roentgens and to the cohos of 40 roentgens. Irradiated, and similarly treated but unirradiated controls, were compared for survival, growth, vertebral numbers and anomalies, opercular defects, and sex ratios. Significant differences were observed only in the more frequent occurrence of opercular defects among irradiated than among control coho salmon smolt. In some phases of growth the controls and in others the irradiated groups showed superiority without a discernible pattern. As late as the time of release of the smolt for their seaward migration, little if any difference appeared between experimental and control groups. Differences will be sought in the F1 generation from these fish.