Effects of triploidy induction using heat shock on the hatching, survival and triploid rate of ornamental koi (Cyprinus carpio koi) larvae

This study was carried out in order to assess the effect of thermal shock on induction of triploidy in Koi carp (Cyprinus carpio koi). Three shock temperatures (38, 40 and 42 °C), five time of initiation of shock (1, 2, 4, 6 and 8 min after fertilization) and three shock durations (1, 2 and 3 min) were tested. A sample of eggs was collected as a control group. There were 46 experimental groups, including 45 treatments and 1 control.The results showed that the highest hatching rate (59.49 %) was obtained in treatments 19 (4 min after fertilization for 1 min at 38 °C), 10 (2 min after fertilization for 1 min at 38 °C) and 28 (6 min after fertilization for 1 min at 38 °C), while there were no significant differences between these treatments and the control (p > 0.05). Also, there was a significant decrease of larvaesurvival rate with increased shock temperature and shock duration (P < 0.05). The best triploidy rate (65.95 %) and triploid yield (63.75 %) were obtained in treatment of 40 ºC for 2 min at 6 min after fertilization (treatment 32). Ratio of erythrocytes and nuclei volume in triploids to diploids was 2.74 and 1.92, respectively. According to the results, it seems that the use of heat shock of 40 ºC, 6 min after fertilization for 2 min can be most effective treatment for induction of triploidy in Koi carp.