Author(s): Parven A., Gallardo W. G

Abstract: Cold shock and heat shock were evaluated for their efficacy as methods of manipulating ploidy in hybrid catfish (C. macrocephalus × C. gariepinus). The most effective method of inducing triploidy was cold shock at 6 oC applied of 25 min which resulted in 87% triploidy with 48% fry survival rate from fertilization to two weeks rearing period. Both of thermal shock treatment initiated 3 minutes after water activation. Cold shock treatment for 30 min or more caused total mortality of embryos. Heat shock at 40 oC for 1 min resulted 42% triploidy with fry survival of 42%. Flow cytometry analysis was used to assess the ploidy level of diploid and triploid larvae in both experiments with blood samples. In growth experiment, growth of triploid was higher than control but lower than the cold shocked (6 oC 25 min) diploid fry, with the survival rate ranging between 63-73% in all treatments after 16 weeks of rearing period. Triploid fish were 15% larger than control; while shocked diploid was 27% larger than control.

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