Xenogenesis is emerging as an innovative technology for hybrid catfish (channel catfish, Ictalurus punctatus ♀×blue catfish, I.furcatus ♂) production, where primordial germ cells (PGC), spermatogonial stem cells (SSCs) or oogonial stem cells (OSCs) are transplanted into infertile host species such as triploid fish to produce xenogens. Currently, donor cells are collected from randomly selected immature fish without having prior knowledge regarding the best donor stage, which is critical to increase the efficiency and success of germ cell transplantation in catfish breeding. Therefore, the current study was carried out with the objective of determining the relationships between quantity of stem cells, total length (TL), total weight (TW), and the level of androgens [testosterone (T) and 11-ketotestosterone (11-KT)] in blue catfish (donor fish). Positive quadratic relationships were observed between TL and the number of extracted live SSCs (r2 = 0.51; P < .0001) as well as TW and the number of live SSCs (r2=0.37; P < .0001), revealing that a TL of 25 to 39.9 cm and TW of 100 to 499.9 g, yield the highest number of extracted live SSCs. Similar to the findings from males, TL (r2 =0.76; P < .0001) and TW (r2 = 0.67; P < .0001), also revealed positive quadratic relationships to the number of extracted live OSCs, where 25 to 39.9 cm and 200 to 600 g females yielded the greatest number of extracted live cells. Positive quadratic relationships were also detected between levels of T (r2 = 0.60; P < .0001), 11-KT (r2 = 0.60; P < .0001) and number of extracted live SSCs in male catfish, where 49 to 51.9 pg/mL of serum T and 37 to 48.9 pg/mL of 11-KT yielded the maximum number of live SSCs. Overall, these relationships between the quantity of stem cells and body size as well as the profile of sex steroid hormones reveal promising results as reliable biomarkers to enhance the efficiency of germ cell transplantation. These results can also be used to make precise predictions on the number of stem cells at a certain body size without sacrificing precious fish housed in living genetic repositories.
