Effect of hot thermal shock in eggs of tilapia nilotica (Oreochromis niloticus): after-fertilization time and duration of the process in the survival of larvae

Abstract

The application of hot thermal shock in the eggs of the Nile tilapia, Oreochromis niloticus, after the fertilization is employed to block the 2nd meiotic division or to inhibit the 1st cleavage. That technique is utilized to produce monosex population, sterile or polyploid. In this study, two assays were realized: 1st, utilizing after-fertilization times of 50, 55 and 60 min and duration of shock of 2 and 5 min; and the 2nd one, with after-fertilization times of 24, 27 and 30 min and duration of shock of 5 and 8 min, in April and December 2003, at the laboratories of CAUNESP/UNESP, Jaboticabal, SP, Brazil. Only the females were induced to spawn with GCH, showing the effectiveness of the process in the production of gametes. Significant differences (P < 0.05) among the treatments (moments of application and duration of the hot thermal shocks) in the two assays had been found, in relation to the estimative of the survival rates. Elevated percent of deformed animals had been registered. The low survival rates observed in the control and in the treatment groups indicate that the artificial induction and incubation (fertilization to hatching) affect the embrionary development of larvae.