Hormonal regulation of oocyte maturation and ovulation in lambari (Astyanax altiparanae) induced by different pituitary extracts

The processes of final oocyte maturation (FOM) and ovulation remain poorly understood in neotropical fish and hypophysation is the most common method to induce these processes in captivity. Therefore, this study aimed to investigate mechanisms controlling FOM and ovulation during hypophysation with carp (CPE) and lambari pituitary extract (LPE), using lambari (Astyanax altiparanae) as a model. A completely randomized experiment was conducted with three treatments, including fractionated doses of 6 mg/kg of CPE or LPE, and a control group injected with saline solution. Females received two intraperitoneal injections and five females per treatment were randomly sampled at six time points to assess plasma DHP and PGF2α levels, ovarian gene expression and histology. Both CPE and LPE reduced lhr expression while increasing hsd20b2 and ptger4b expression and plasma DHP levels, ultimately leading to FOM and ovulation. This suggests that Lh receptor activation in follicular cells triggers hsd20b2 synthesis, promoting DHP production and release. In contrast, no significant molecular and hormonal changes were observed in the control, which exhibited low levels of germinal vesicle breakdown (GVBD) and post-ovulatory follicles (POF). A positive correlation among DHP levels, GVBD, and POF further underscored their association with FOM and ovulation. Overall, hypophysation with either CPE or LPE effectively induces FOM and ovulation, thereby enhancing productivity in lambari. However, our findings indicate that LPE achieves greater synchronization of FOM and ovulation events across females. Additionally, as a locally sourced product, LPE may present a more economically viable option for Brazilian aquaculture.