Comparison of cold and heat shocks to induce diploid gynogenesis in Thai walking catfish (

Large numbers of female broodstock (Clarias macrocephalus) are required cach year to produce hybrid catfish which retain the materna1 meat quality of Thai walking catfish and the paternal fast growing and disease resistant traits of the African catfish (C1arias gariepinus). Therefore, diploid meiotic gynogens were induced in Thai walking catfish and their potential use for aquaculture was evaluated. Induction was performed using UV-irradiated sperm of stripped catfish (Pangasius sutchi) followed by either cold or heat shock at 4.5 min after activation. Heat shock at 42 °C for 1 min was the best among various heat shock regimes. Cold shock (7 °C for 14 min) gave significantly higher percentages of meiotic diploid fry (26-41%) than the heat shock (12-26%). Six-month-old meiotic gynogens were all female and showed slightly inferior growth to male and femalc controls. The six-month-old control-males and females and the gynogens were not different in size. Survival of the gynogens (73 ± 8 %) was slightly inferior to the mixed sex control (87 ± 10 %). Gonado-somatic index of gynogens at 1 year of age (5.7%) was slightly inferior to that of the control female (8.8 9%). Therefore, the direct use of all female meiotic gynogens to enhance production of Thai walking catfish, may be doubtful. However, their use for breeding purposes is promising providing that inbreeding depression is eliminated.