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Intravenous (IV) injection is widely recognized as the most effective and commonly utilized method for achieving systemic delivery of substances in mammalian research models. However, its application in adult zebrafish for drug delivery, stem cell transplantation, and regenerative and cancer studies has been limited due to the challenges posed by their small body size and intricate blood vessels. To overcome these limitations, alternative injection techniques such as intracardiac and retro-orbital (RO) injection have been explored in the past for stem cell transplantation in adult zebrafish. However, these techniques have their drawbacks, including the need for meticulous injection techniques or increased risk of mortality. In this study, we have developed a refined and optimized IV injection procedure specifically tailored to adult zebrafish, addressing the challenges associated with their unique anatomy. To demonstrate the effectiveness of this technique, we performed successful IV injections of whole kidney marrow cells from Tg(mpo: EGFP) fish and FITC-dextran dye into adult Casper fish. The subsequent visualization of injected cells and dyes using a fluorescence microscope confirmed their successful delivery and engraftment within the zebrafish. Furthermore, we demonstrated that compared with the intracardiac and RO injections, the IV injection resulted in improved survival rates and engraftment efficiency in treated zebrafish. This approach enables precise delivery and localization of substances and holds great potential for large-scale drug and chemical screening using adult zebrafish. Additionally, the ability to visually track the injected cells and dyes provides invaluable insights into their engraftment, migration, and interactions with host tissues, enabling a more comprehensive evaluation of therapeutic effects and biological processes in zebrafish models.