A single recombinant follicle stimulating hormone injection promotes spermatogenesis onset in a proportion of juvenile flathead grey mullet Mugil cephalus

Recombinant gonadotropins have proven effective in overcoming the reproductive dysfunction observed in adult captive flathead grey mullet Mugil cephalus . This study aimed to assess the effectiveness of recombinant follicle-stimulating hormone (rFsh) in inducing early puberty in this species, while also improving our understanding of the role of Fsh in spermatogonial self-renewal, proliferation, progression towards spermatogenesis, and testicular apoptosis. Juveniles (338.1 ± 47.1 g) were assigned to three groups: an untreated control group (group C-0; N = 9), a saline-injected control group sampled 7 days after injection (group C-7; N = 9), and a group receiving a single Mugil cephalus -rFsh injection (12 µg kg⁻¹) and sampled 7 days after injection (group rFsh-T; N = 10). Four individuals of the rFsh-T group exhibited higher gonadosomatic index, enlarged seminiferous tubules, and histological signs of advanced spermatogenesis compared to the control groups. These responders exhibited reduced densities of dividing undifferentiated spermatogonia, increased densities of committed spermatogonia, elevated plasma 11-ketotestosterone (11-KT), and a higher 11-KT/17β-estradiol (E2) ratio. Apoptosis was negligible across all groups, except for one rFsh-responsive fish displaying sparse apoptotic spermatogonia and Sertoli cells. These findings indicate rFsh successfully initiated spermatogenesis in 40% of treated fish by stimulating 11-KT secretion and increasing the 11-KT/E2 ratio, which in turn promoted spermatogonial proliferation towards meiosis. Finally, the study demonstrates that undifferentiated spermatogonia are not significantly affected by apoptosis in juvenile flathead grey mullet, contributing to a deeper understanding of testicular apoptosis patterns in seasonally reproducing fish.