In this article, we have introduced a novel germ cell transplantation technique for use in fish. These experiments have combined the following biological characteristics of living organisms to build an effective method: (i) newly hatched fish embryos are immunologically immature; (ii) germ cells can seek out and migrate to gonads; (iii) fish spermatogonia differentiate into eggs as well as sperm; and (iv) although triploid fish are sterile, their somatic cells are normal. This transplantation procedure is both simple and rapid, enabling us to transplant into 30–50 newly hatched recipients in an hour.
Recently, successful transplantation of spermatogonia into the testes of adult recipients has been performed in tilapia (Lacerda et al. 2006, 2010, 2012), pejerrey (Majhi et al. 2009) and zebrafish (Nóbrega et al. 2010). If these techniques can become applicable to the production of donor-derived eggs, they would also be useful in the creation of surrogate broodstock and preservation of genetic resources in fish. Furthermore, the development of methods for the in vitro culture of spermatogonia in several fish species could improve the efficiency of germ cell transplantation because donor cells could be amplified in vitro prior to use (Hong et al. 2004; Shikina et al. 2008; Shikina and Yoshizaki 2010). Other improvements include our identification of a cell surface protein that is predominantly expressed in rainbow trout ASG (Nagasawa et al. 2010), which could enable the enrichment of ASG from fish testes using specific antibody-mediated flow cytometry or magnetic cell sorting. Finally, we recently developed a simple flow cytometry protocol to enrich ASG using light scattering properties (Kise et al. 2012). We predict that these research efforts will lead to rapid advances in novel developmental biotechnology for aquacultural and conservation applications.