In a recently established system for intraperitoneal spermatogonial cell transplantation in salmonids, donor type A spermatogonia (type A SG) were microinjected into the peritoneal cavity of newly hatched larvae. Compared with salmonids, the larvae of marine teleosts are small and vulnerable to physiological and physical stresses, making it difficult to use them for cell manipulation. Herein, we developed type A SG cell transplantation in Nibe croaker (Nibea mitsukurii) by optimizing 1) the developmental stage of the donor testes used to prepare type A SG-enriched cell suspensions and 2) the timing and location of intraperitoneal cell transplantations to recipient larvae. Donor cells labeled with PKH26 fluorescent dye were transplanted into the peritoneal cavity of 3-, 4-, 5-, and 6-mm larvae using glass micropipettes. Consequently, 20.6% of the 4-mm larvae recipients survived for 3 wk, and 36.3% of the survivors had donor-derived cells in their gonads. The incorporated donor cells were identified as germ cells by germ cell-specific nuclear morphology and expression of a germ cell marker. In contrast, no donor type A SG were incorporated into the gonads of 6-mm recipient larvae. These data indicate that there is a distinct narrow window in the developmental stages of recipient larvae when exogenous type A SG can be incorporated into the gonads. The establishment of this system in pelagic egg-spawning marine teleosts would allow the creation of a new broodstock system in which a target species with a large body size and long generation time could be produced from related species with a small body size and short generation time.