Maturation of viable fish eggs ex vivo remains a challenging, but realistic objective, for the conservation and research community. Arguably a less technically ambitious aim in biological terms is to construct an ex vivo microenvironment that favours development of FGSCs into mature oocytes that can match the taste and mouthfeel of caviar. Our proprietary, 3D-printed, ex vivo fish ovary analogue also represents a valuable platform technology in the fields of aquaculture and conservation of biodiversity.

Fig. 1. - Production of functional eggs and sperm from in vitro-expanded ASGs by ASG transplantation. b Eggs produced by triploid female recipients that received expanded ASGs in culture (Cul-TP) or wild-type diploid female trout (2N cont). c Milt produced by wild-type diploid trout (2N cont), triploid trout (3N cont), male recipient trout that received in vitro-expanded ASGs (Cul-TP), or male recipient trout that received freshly prepared testicular cells (Non-cul-TP). Therefore, the method of in vitro expansion of ASGs established in this study is a breakthrough for these situations. Combination of in vitro expansion, cryopreservation, and transplantation of  ASGs can be utilized to rescue fish species on the verge of extinction. *Takahashi et al. 2020