Decreased wall shear stress was detected in β-lapachone-treated embryos. Tg(gata1:DsRed) was treated with DMSO or β-lapachone for 4 h at 24 h post-fertilization (hpf), and blood cell circulation was recorded at 30 hpf. A: A DIC image of 30-hpf embryos is shown. The inset figure in panel A indicates the recorded region, and DsRed-labeled erythrocytes were recorded under the TRITC mode (a-f). Images corresponding to an individual DsRed-labeled erythrocyte (arrow) at time 0 and after traveling for some distance at time t are shown for respective DMSO-treated (a, b) and 2 representative β-lapachone-treated (c, d; e, f) embryos. B: The relative wall shear stress was calculated based on τ = 4 μQ/πR3 where μ is viscosity, Q is the flow rate, and R is the blood vessel diameter. Student's t-test was used to compare DMSO- and β-lapachone-treated embryos. * p < 0.01.