<p>Xenogenic individuals are sterilized hosts that are colonized by germ cells transplanted from a donor species and can subsequently produce donor-derived gametes. In our case, unsorted gonadal cells from a donor species injected near the genital ridge of a sterile surrogate should colonize only that region, eventually becoming donor gametes. Unsorted gonadal cells from blue catfish (<i>Ictalurus furcatus</i>) injected into triploid common carp (<i>Cyprinus carpio</i>) embryos and fry were detected by PCR assays predominantly in recipient gonads and, in a subset of individuals, occasionally in DNA extracts from pectoral fin, anal fin, or muscle tissue, resulting in mosaicism in these tissues (presence of donor DNA/cells). Recipients retained normal common carp morphology. Donor signal was not detected in other assayed tissues, including eyes, livers, intestines, and hearts. This is the first report of such aberrant, presumably gonadal stem cell migration and colonization outside the gonads in xenogenic fish. Individuals injected later in development had reduced or no mosaicism compared to those injected at early developmental stages. Catfish donor cells were detected in the gonad, muscle, anal fin, and pectoral fin of both diploid and triploid common carp hosts. The incidence of non-target tissues containing blue catfish DNA trended towards being higher in triploids than diploids, especially when mosaicism involved three tissues. These findings provide preliminary insights into donor unsorted gonadal cell migration, tissue-specific persistence, and developmental timing in reproductive biology. These PCR findings indicate tissue mosaicism but do not establish somatic differentiation.</p>