Polyploidy induced by heat shock in channel catfish

Female channel catfish were induced to ovulate in fiberglass raceways by administering a total dose of 11 mg/kg of carp pituitary extract in two injections. Eggs were handstripped and fertilized with minced testis from donor males. First cleavage division was visible and occurred around 90 min postfertilization. Eggs were heat shocked in 56-1 aquaria at 80, 85, or 90 min postfertilization at temperatures of 40, 41, 42, or 43°C for a duration of 1, 2, 3, or 4 min.Eggs subjected to heat shock produced tetraploids, triploids, diploids, and mosaics. Ploidy level was determined by counts of chromosome preparations of five embryos per treatment combination sampled prior to hatching. Eggs stressed at 42 and 43°C had nearly complete mortality in shocks longer than 1 min. Forty-one degrees and 3 min duration induced tetraploidy in 62% of the embryos sampled. In shocks of 3 and 4 min at 40 and 41°C, postfertilization time did not significantly affect rates of polyploid generation. Hatchability was low in treatments which induced tetraploidy but no abnormalities were found among sampled embryos. Live fry from these groups are being raised for further study.