Direct impact of ambient (1.95 W/m²) and subambient doses of UV-B radiation on muscle/skin tissue antioxidant status was assessed in mature zebrafish (Brachydanio rerio). The influence of these doses on hatching success and survival in earlier life stages was also examined. Subambient doses of UV-B radiation in the presence (1.28 W/m²) and absence (1.72 W/m²) of a cellulose acetate filter significantly depressed muscle/skin total glutathione^† (TGSH) levels compared with controls (0.15 W/m²) and low (0.19 W/m²) UV-B–treated fish after 6 and 12 h cumulative exposure. Ambient UV-B exposure significantly decreased muscle/skin glutathione peroxidase (GPx) activity after a 6 h exposure; activities of glutathione reductase (GR) were unchanged over this exposure period. Superoxide dismutase (SOD) and catalase activities peaked after 6 and 12 h cumulative exposure, respectively, but fell back to control levels by the end of the exposure period. The changes in tissue antioxidant status suggested UV-B–mediated increases in cytosolic superoxide anion radicals (O₂⁻) and hydrogen peroxide (H₂O₂). This apparent UV-B–mediated increase in oxidative stress is further supported by a significant increase in muscle/skin thiobarbituric acid reactive substances (TBARS). Hatching success of newly fertilized eggs continuously exposed to ambient UV-B was only 2% of the control value. Even at 30 and 50% of ambient UV-B, hatching success was only 80 and 20%, respectively, of the control. Newly hatched larvae exposed to an ambient dose of UV-B, experienced 100% mortality after a 12 h cumulative exposure period. This study supports a major impact of UV-B on both the mature and embryonic zebrafish.