TEN YEARS OF STUDIES ON THE USE OF PGF2a AS A TOOL FOR IMPROVING Piaractus mesopotamicus OVULATION

Here we present a synthesis of ten years of efforts to mitigate pacu ovulation failures, as well as new results on the dose-dependent effect of prostaglandin F2α (PGF2α ) on  the ovulation rate of the species. Pacu belongs to a group of fish called "roundfish " (medium size characiformes ) which is the second most produced fish group in Brazil. In captivity, the spawning of pacu is only achieved by means of hormonal induction.

To increase ovulation success, we initially associated with hypophysation the co-administration of PGF_2α (2 mL.fish^-1 Ciosin®, equivalent to 0.25 mg.mL^-1 cloprostenol) at the time of the second hormonal dose. In spite of improving ovulation, some females continued to have low fecundity, mainly associated with delayed ovulation. Thus, in order to increase plasma PGF_2α levels at ovulation, we injected PGF_2α after the second hypophisation dose. However, the results were not satisfactory since, probably due to the need for another management intervention, neither the expected improvement in ovulation rates was observed, nor the PGF_2α plasma levels were higher as expected. Thus, we tested the use of increasing and equidistant doses of PGF_2α (1 mL.kg^-1 to 7 mL.kg^-1 of Ciosin®); and the best results were obtained using 5.5 mL.kg^-1 of Ciosin® (1.37 mg.kg^-1 of cloprostenol.kg^-1). This treatment provided 100% spawning and no bad unsuccessful spawn (relative fecundity < 30 g/kg (egg mass/female mass)) (Table 1). The latency period (ATU) was stable among groups (Table 1), but fecundity, fertility and hatching rates were favorable using 5.5 mL.kg^-1 Ciosin® (Table 1). Corroborating several previous studies in other species, we preliminary concluded that successful spawning may be more associated with longer exposures to high PGF_2α plasma concentrations than to a peak of this substance at ovulation.