In humans and in zebrafish, the organs that make eggs and sperm (gonads) first develop with the ability to become either an ovary making eggs or a testis making sperm. In humans and many other animals, a single gene causes the gonad to develop in one direction or the other. We wondered how this process works in zebrafish, a major model for research on the mechanisms of embryonic development, physiology, behavior, and neuroscience. The graphic novel entitled ‘The mystery of zebrafish gonad development’, explains research on how a zebrafish gonad decides to become an ovary or a testis. This material is based upon work supported by the Office of Polar Programs at the National Science Foundation under NSF grant number OPP-2232891 and the National Institutes of Health Grants No. R35GM139635, R01GM085318, and R01OD011116. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the National Institutes of Health. This comic was created as part of the University of Oregon Science and Comics Initiative. (https://opentext.uoregon.edu/science-comics/) Our previous short scientific graphic novels are also publicly available! “What controls sex development in fish?” in ten languages! (https://blogs.uoregon.edu/fishsexdetermination/) “A mysterious disease in Antarctic fish” in five languages! (https://blogs.uoregon.edu/antarcticxcell/) “What cool fish live in icy Antarctica?” in ten languages! (https://zenodo.org/records/14253745)