Is the hybrid tiger trout a suitable recipient for the transplantation of salmonid spermatogonia?

In this study, we tested the utility of sterile tiger trout, an interspecific hybrid of a brown trout ( Salmo trutta m. fario ) female and a brook trout ( Salvelinus fontinalis ) male primarily bred for aquaculture, as a potential recipient for the surrogate production of other salmonid fish. The sterility of adult tiger trouts was confirmed as spermatogenesis progressed further from the mitotic phase in only one male, while only a few females contained vitellogenic oocytes. We transplanted spermatogonial stem cells (SSCs) from rainbow trout into larvae (total of 371 recipients) and adult (total of 15 recipients) tiger trout. Recipients were reared up to 3 years post-transplantation (ypt), and transplantation success was tested by (1) the production of functional gametes, (2) development of recipient gonads past the baseline development assessed through histological analyses and (3) detection of donor cells inside of recipient gonads through molecular analyses. Gametes were produced only by one male recipient in which SSCs were transplanted as a larva. This male displayed clear signs of a developed testis, and rainbow trout DNA was detected in the testicular samples. Rainbow trout DNA was detected in three additional male recipients (injected as larvae), however, none of these individuals displayed signs of gametogenesis progression at 3 ypt. Furthermore, recipients injected as adults did not show any progression of gametogenesis, nor the presence of rainbow trout DNA in the gonads at 2.5 ypt. Milt obtained by the mentioned recipient was used to fertilize rainbow trout eggs which led to the production of donor-derived offspring. All viable offspring displayed phenotypical characteristics of rainbow trout which was further corroborated by molecular analyses. In conclusion, we display that the hybrid tiger trout can be used for the surrogate production of other salmonid fish, especially trout species which are closely related. • Hybrid tiger trout was tested as a recipient in surrogate broodstock technology. • Rainbow trout spermatogonia were transplanted into larvae and adult tiger trout. • Donor-derived gametes were produced by a male recipient injected as a larva. • Donor-derived progeny was successfully produced. • None of the recipients injected as adults displayed gametogenesis progression.