Optimal heat shock condition for tetraploidy induction in rainbow trout (Oncorhynchus mykiss)

Tetraploid rainbow trout has a key role in producing infertile triploid fish by indirect method and introducing them in cultivation system. The purpose of the present study was to determine the optimal heat shock for tetraploidy induction in rainbow trout with emphasis on egg size. The efficiency of different shock temperatures: 28, 30 and 32 °C, durations: 1, 5 and 10 min and starting time: 45, 55, 65, 75 and 85 degree-hour post fertilization (dhPF) on two different egg size diameters (4.2 ± 0.12 and 5.5 ± 0.20 mm) for tetraploidy induction in rainbow trout were analyzed. Tetraploidy rates were determined using red blood cell sizes as well as number of nucleolar organizing regions (NORs) at swim up stage. Tetraploidy rates were in the range of 18-69 and 18-76 % for the groups of eggs over and less than 5 mm in diameter respectively. The statistical analysis showed that the highest tetraploidy efficiency (13%) for the larger egg size achieved by treating eggs at 28°C, for 10 min starting at 65dhPF. While for the smaller egg size, the highest efficacy (7%) was observed in group treated at 28°C, for 5 min starting at 75 dhPF. Although tetraploidy induction has been done previously in rainbow trout, for the first time, the results of this study showd that tetraploidy efficacy was affected by egg size as well as other shock related parameters.