Our findings complement recent studies that describe the labeling, biodistribution, and potential functional roles of exogenous tumor derived and endogenous CD63+ EVs in larval zebrafish.24,28 Additionally, we have provided the first cryo-EM assessment of total larval and adult zebrafish cardiac EVs, which reveals size distributions reminiscent of EVs from other species and cell types48,49 and highlights the plethora of different EV morphologies found in vivo. This evidence concerns the gene CD63 and neoplasm.