Effect of Aging Silver Carp (Hypophthalmichthys molitrix) Ova In Vitro on Offspring Viability Rates (Beni Mellal Hatchery, Morocco)

The quality of the silver carp (Hypophthalmichthys molitrix) eggs is important during artificial reproduction. This quality influences the tolerance of eggs to survive in vitro after ovulation and before fertilization. This tolerance of eggs to storage conditions has significant effect on the viability rates of the offspring (fertilization rate, embryo survival rate, larval survival rate and fry survival rate). It is most often recommended that eggs be collected and fertilized immediately after ovulation during seed production. In practice, however, several females injected with pituitary extract hormones will ovulate at the same time, so the collection of eggs of some females must be postponed. The handling of each female takes about 15 to 20 minutes, and the interval between the fertilization of the eggs of the first and the last female is usually more than 60 minutes. During this time, eggs gradually age. The aim of this study was to quantify the maximum in vitro residence time of eggs after which they remain suitable for fertilization and to give acceptable progeny viability rates. The study was carried out at the Beni Mellal hatchery in Morocco using 20 females weighing between 2.9 and 9.4kg. Their eggs were fertilized at different time intervals after ovulation (0.30, 60, 90 and 120min). The results obtained show that the viability rates of the offspring are acceptable up to the limit of 45min at 18°C. In order to avoid this aging phenomenon, it is advisable to work in small groups with a reduced number of females and to shift the time intervals between hormone injections.