SOME EFFECTS OF ULTRAVIOLET RADIATION ON SOCKEYE SALMON EGGS AND ALEVINS

Abstract

Ultraviolet radiation of wave lengths from 2800 Å to 3100 Å, generated by a General Electric RS sun lamp, was used to irradiate eggs and alevins of the sockeye salmon (Oncorhynchus nerka). Mortality curves are presented for a series of measured dosages. Irradiation of eggs in the later stages of development produced a stimulating effect on the rate of hatching. These premature alevins, which hatched a month before the controls, were abnormal in several respects. The vertebral column was curved downward over the region of the heart, growth was retarded, the yolk was not utilized as rapidly as in the controls and pigmentation was delayed. The mortality was particularly high at the time of hatching and the process was abnormal. Histological examination of irradiated alevins revealed changes in the epidermis and fibroelastic layers of the skin. These were localized to the irradiated regions. Heavy doses produced severe degeneration of the epidermal layer with the formation of granules in the nuclei, the breakdown of the goblet cells, and subsequent desquamation. The changes were less extreme with lower dosages and in these fish a recovery began about 13 days after irradiation. Internal organs and tissues beneath the fibroelastic layers of the skin were not visibly affected by the irradiation.