Effects of the time of administration and the concentration of exogenous prostaglandin F on ovulation in pacu

Abstract In this study, we evaluated the effects of applying Ciosin® (containing 0.25 mg/ml cloprostenol, an analogue of prostaglandin F 2α (PGF 2α )) at the time, five or seven hours after hypophysation resolving dose (experiment 1). In the experiment 2, at the time of hypophysation resolving dose, females were induced with 1.0 to 7.0 mL Ciosin /kg. Reproductive parameters and plasma levels of 17α-20β-dihydroxy-4-pregnen-3-one (DHP) and PGF 2α were evaluated at the time of spawning for both experiments. Neither the timing of Ciosin application closer to the spawning nor its higher concentrations resulted in increased reproductive parameters or elevated PGF 2α and DHP plasma levels. The absence of PGF 2α peak at the time of ovulation in both experiments can be attributed to the rapid increase and subsequent decrease in exogenous PGF 2α levels shortly after application. Interestingly, multivariate analysis in experiment 2 revealed two main clusters: one characterized by spawning failure, poor-quality spawns and low DHP levels; and the other by showing successful spawning, high fecundity and elevated DHP levels. Since it is known that the DHP binding to the nuclear progestin receptor induces prostaglandin receptor expression, these facts may explain why better reproductive performances were associated with higher endogenous DHP levels, but not with changes in exogenous PGF 2α application. Although positive correlations were observed between DHP levels and good reproductive performance, the reasons behind the substantial variation in DHP levels among females subjected to the same treatments remain unknow. An emerging focus is to elucidate the pattern of expression of PGF 2α receptors and its relationship with DHP in Piaractus mesopoatamicus.