Ovulation rate, latency period and ova viability after GnRH- or hCG-induced breeding in the Asian catfish Pangasius hypophthalmus (Siluriformes, Pangasiidae)

Over a 3-year period at the Sukamandi station (West Java, Indonesia), 107 P angasius hypophthalmus females were selected on the basis of a modal oocyte diameter greater than 1.0 mm and treated with either Ovaprim (n = 97) or h CG (n = 10) to induce oocyte maturation and ovulation. The two hormonal tre atments led to similar results in terms of ovulation rate (88 and 90 %), ha tching rate (72 +/- 25 and 82 +/- 11 %) and relative fecundity (171 000 +/- 73 000 and 128 000 +/- 60 000 ova.kg(-1), with Ovaprim and hCG, respective ly). The latency period between the last hormone injection and ovulation wa s negatively correlated to water temperature but showed important variation s at a same temperature depending on individual females (e.g. between 5 and 11 h at 28-29 degrees C). The ovulation time was therefore difficult to pr edict accurately in this species. The assessment of the viability of ova re tained in the ovarian cavity after ovulation showed that the process of ove rripening occurs rapidly in P. hypophthalmus. The overall quality of ova be gan to decline as early as 2 h after ovulation and, after 3 h, hatching rat es decreased and the proportion of deformed larvae increased significantly in comparison to those observed at the time of ovulation. In some individua l females this process occurred even more rapidly, with a sharp decrease in hatching rates between 1 and 2 h post-ovulation. The duration of ova survi val did not appear to depend on the type of hormone treatment used to induc e ovulation (Ovaprim or hCG). For optimized gamete management ill hatcherie s, it is therefore recommended to check carefully the females for the occur rence of ovulation (between 3 and 11 h after the last hormone injection, de pending on water temperature) and to strip and fertilize the eggs less than 2 h thereafter. (C) 2000 Ifremer/Cnrs/Inra/Ird/Cemagref/Editions scientifi ques et medicales Elsevier SAS.