The flow cytometer was used to compare the DNA content in the blood cells and sperm in the new type of tetraploid (G 1×4n) and in red crucian carp used as the control. The new type of tetraploid (G 1×4n) was produced by mating the diploid female gynogenetic progeny (first generation,G 1) of the tetraploid hybrid of red crucain carp × common carp, with the male of the tetraploid hybrid. Chromosome spreads from the kidney tissue in the new type of tetraploid were also examined. The results from the flow cytometer indicated that the mean DNA content of the diploid sperm produced by the new type of tetraploid was twice that of the haploid sperm generated by the diploid red crucian carp, and the mean DNA content of the blood cells in the tetraploid was twice that in red crucian carp. Examination of chromosome spreads from the kidney tissue also indicated that the examined samples of the G 1×4n were tetraploids with 200 chromosomes, which was in agreement with the results of the DNA content measurements from the sperm and the blood cells. The present study proved that the new type of tetraploids was able to produce normal diploid sperm, which fertilized diploid eggs from the new type of tetraploid to produce viable offspring. The flow cytometer was proved to be one of the accurate, secure and simple methods to distinguish the different ploidy fish in blood cells and sperm by measuring their DNA content .
