Towards a standardized in vitro ovulation induction protocol for lambari (Astyanax altiparanae) using DHP and PGF2α

This study aimed to evaluate the in vitro ovulation in lambari ( Astyanax altiparanae ) by 17α,20β-dihydroxy-4-pregnen-3-one (DHP) and prostaglandin F 2α (PGF 2α ). Five experiments were carried out to: (1) test different DHP concentrations (0.01–100 μg/mL), (2) assess the influence of pH (7.1 vs. 9.0) with medium exchange, (3) compare responses between isolated follicles and ovarian fragments, (4) analyze the effect of medium replacement during induction, and (5) examine ovulation induced by DHP alone or combined with varying PGF 2α doses (50–5000 ng/mL). The results showed that DHP promotes ovulation in lambari, but its efficacy is hindered when using ovarian fragments instead of individualized follicles. Both pH 7.1 and 9.0 supported ovulation similarly when using 1 μg DHP/mL, and medium exchange was not necessary for successful induction. Additionally, PGF 2α combined with DHP did not enhance ovulation compared to DHP alone, though PGF 2α alone induced ovulation in a dose-dependent manner, with 5000 ng/mL being sufficient. These findings confirm that both DHP and PGF 2α are potent inducers of final maturation and ovulation in lambari in vitro . Moreover, the potential synergistic effect observed at higher PGF 2α doses underscores the importance of dose standardization when using hormonal combinations to prevent spawning failure in captive females. Prostaglandins are used as a complement to hypophysation to enhance ovulation in farmed fish species. A dose-dependent effect of PGF 2α observed here suggests potential for improving lambari in vivo ovulation rates that nowadays are reported to be around 40–60% using the best protocols.