Hormonal induction of final maturation and ovulation in the sábalo, Prochilodus platensis Holmberg: Treatments, latency and incubation times and viability of ovules retained in the ovary after ovulation

Final maturation and ovulation were consistently induced in female sábalo by applying single doses of homologous pituitary extracts (PPit) (0.5–1 PPit/kg live weight) or mixtures of pituitary extract with human chorionic gonadotropin ((0.5 PPit + 250 IU HCG)/kg; (1 PPit + 500 IU HCG)/kg). No positive responses were observed in females in which HCG only was applied in doses up to 1000 IU/kg. Stripping and dry fertilization of the ovules produced viable larvae; mean fertilization and hatching rates were 85% and 80%, respectively. Latent period between injection and ovulation decreased from about 12 h at 24.5°C to 9 h at 28°C. Incubation time varied according to temperature between 17 h at 25°C and 12 h at 28°C. Highest hatching rates, and lowest proportions of deformed larvae, were obtained when stripping and fertilization were performed immediately after ovulation. Delays greater than 1 h resulted in decreasing hatching rates and increasing proportions of malformed larvae. For example, artificial fertilization of ovules retained in the ovarian cavity for more than 2 h (at 26°C) produced mean hatching rates under 20% and over 40% malformed larvae.