For live imaging of zebrafish, selected embryos were mounted in low melting point (LMP) agarose (1%, wt/vol) at the bottom of a 29 mm glass bottom dish and covered with fish water at 33°C. Digital micrographs or real‐time tracking images were taken either with a Zeiss Imager.Z1 fluorescence microscope (Carl Zeiss, Germany) or a Leica SP5 resonant scanning confocal (Leica, Germany). Super‐resolution imaging of F‐actin formation in living CTCs in zebrafish was obtained byZeiss LSM 880 Confocal Microscope with Airyscan (Carl Zeiss, Germany). For the entire mouse lung lobes and zebrafish body images, both fluorescent and bright‐field images were taken by Zeiss SteREO Discovery.V20 stereomicroscope (Carl Zeiss, Germany). The tumor size, CTC diameter and actin filaments density analysis were based on fluorescent images and quantified by the corresponding imaging software.