Optimal conditions for the induction of triploidy in the sea bass ( Dicentrarchus labrax L.)

Abstract

The optimal conditions for the induction of triploidy in the European sea bass ( Dicentrarchus labrax L.) using cold shocks were investigated. Three treatment variables were considered: the time after fertilization when the shock was applied, the temperature of the shock and the duration of the shock. Ploidy was determined by counting the nuclear organizer regions, karyotype analysis and measures of erythrocyte size. A first series of experiments performed at what was subsequently shown to be a sub-optimal shock duration (5 min), demonstrated that the best time after fertilization for cold shock application was 5 min, regardless of temperature of shock (0 or 2 °C). The maximum percent of triploids obtained was 87% at survival rates approximately 90% of that of the untreated controls. In a second series of experiments, this timing (5 min after fertilization) was used to determine the best combination of temperature (0, 2 or 4 °C) and duration of shock (5, 10, 15 or 20 min) for optimal triploid induction. In these experiments, triploidy reached 100%, with survival approximately 80% of controls. However, when the shock temperature was above 0 °C and the duration shorter than 10 min, triploidy induction became highly variable. The optimum treatment parameters for the induction of triploidy in the sea bass were established to be as follows: time after fertilization, 5 min; duration of shock, 10 min; temperature of shock, 0 °C. Pre-shock incubation temperature was 12–13 °C in all cases. These conditions were used to mass-produce triploid sea bass. Results showed that under these conditions triploidy induction could reach 100%, although it was essential to reproduce optimum shock conditions, especially temperature, when dealing with large volumes of eggs. At 8 months of age, triploid sea bass had similar growth than their diploid counterparts. In conclusion, this paper presents the optimal conditions for triploidy induction in the sea bass using cold shock and indicates that it is possible to mass-produce triploids of this commercially important species.