Tetraploidy in Rhamdia quelen (Quoy and Gaimard 1824) by a dual thermal shock (heat and cold)

Abstract

The efficiency of double thermal shock to induce tetraploidy in Rhamdia quelen (jundiá) at different post-fertilization periods was assessed. Each test was performed with 20 mL of eggs (10, 15, 20, 25, 30 and 35 mpf í  minutes post-fertilization) exposed to hot thermal shock (39 ± 0.2°C) for 3 min, followed by cold thermal shock (1.0 ± 0.1°C) for 30 min. A control group was also employed. Fertilization and hatching rates were evaluated 12 and 30 hours post-fertilization (hpf) respectively. After 60 hpf, twenty-five larvae from each experimental unit were fixed to verify the ploidy by flow cytometry. Control fertilization rate was 87.83% and reached 23.4%, 28.5%, 30.4%, 20.0%, 30.3% and 36.7%, respectively for 10, 15, 20, 25, 30 and 35 mpf. Tetraploids were detected only at 15 mpf and 20 mpf. This is the first research of tetraploidy in jundiá obtained by hot and cold shocks, making possible the improvement of this technique.