Genetic (DNA) inactivation of fish sperm with ultraviolet irradiation is generally accompanied by a paradoxical effect on survival rates (Hertwig effect). In the present study, sperm samples from ten male bullseye puffer fish (Sphoeroides annulatus) were diluted 1:50 using Cortland's extender solution and used to test the effect of nine ultraviolet doses (0.2–1.0 J cm–2) on motility time in seconds, motility index, and embryo survival rate after fertilizing eggs from five bullseye puffer females. Motility time of sperm irradiated with 0.2–0.9 J cm–2 were not statistically different from the controls, but sperm irradiated with a dosage of 1.0 J cm–2 dosage had significant lower motility time. Motility indices (MI) allowed for the statistical differentiation of four groups in relation to their response to different radiation doses: the first had high MI, and included the controls and 0.2–0.3 J cm–2 treatments; the second had lower MI and included the 0.4–0.7 J cm–2 treatments; the third showed recovery of MI and included the 0.8–0.9 J cm–2 treatments; and the fourth showed the lowest MI with the 1.0 J cm–2 treatment. Embryo survival was highest for the controls and 0.2 J cm–2 treatment, decreasing in the 0.3–0.4 J cm–2 treatments, increasing again in the 0.5–0.8 J cm–2 treatments, until reaching lowest survival in the 0.9–1.0 J cm–2 treatments. These results indicate that the best ultraviolet dosage to achieve genetic inactivation of sperm of this species is close to 0.7 J cm–2, a dosage in which fish fry showed typical haploid syndrome characteristics.