Summary of distinct waves of T lymphopoiesis in zebrafish. (A) A schematic diagram illustrates that EHT occurs along the entire ventral endothelium of the aorta in zebrafish. Blood vessels are marked by light blue. Direction of blood flow is indicated by dark blue dashed arrows. Boundary of the yolk sac in the ventral side of the trunk is depicted by gray dashed line. Hemogenic endothelium of aorta (HEA) is indicated in dark red. The capacity of generating HSCs and HSC-independent T cell progenitors along the HEA are indicated by red and orange bar, respectively. (B) A schematic diagram depicts two waves of T lymphopoiesis in zebrafish. HSC-independent T cells (orange) emerge at 3 dpf and gradually decline at the late larval stages and diminish in juvenile and adulthood. HSC-derived T cells (red) emerge at around 8 dpf and are replenished continuously throughout the life span of zebrafish.