Young zebrafish thrombocytes. (A) Demonstration of newly synthesized young thrombocytes. Top row shows images of zebrafish thrombocytes (young and mature thrombocytes are marked by black and red arrows, respectively); bottom row, red cells. From left to right are the images under bright field, fluorescence with excitation at 450 nm to 490 nm (BrdU uptake shown by anti-BrdU FITC green fluorescence), and fluorescence with excitation at 510 nm to 560 nm (DiI red fluorescence) using a Nikon Optiphot phase-contrast fluorescence microscope. (B) Comparison of young thrombocytes with young human platelets. Top row shows images of human platelets; bottom row, images of zebrafish thrombocytes. Images from left to right are under bright field, fluorescence with excitation at 450 nm to 490 nm (TO fluorescence) and fluorescence with excitation at 510 nm to 560 nm (DiI fluorescence) using a Nikon Optiphot phase-contrast fluorescence microscope. Black arrows show young thrombocytes and young human platelets and red arrows show mature thrombocytes and mature human platelets. The other cells in the field are zebrafish erythrocytes (bottom row) or human red cells (top row).