Abstract: Hybridization between red common carp and grass carp was conducted. The hybrid, a tetraploid through automultiplication of chromosomes, posses feature and habit like maternal parent and can develop into both sexes. The female and male hybrids F1 when backcrossed with both sexes of grass carp, produce triploid offsprings containing 98 chromosomes, but their feature and habit are different. The backcrossing offsprings from female grass carp and male hybrid F1 are herbivorous like grass carp. However, backcrossing offsprings from female hybrid F1 and male grass carp separate into two types: common carp-like or grass carp-like. Common carp-Like of backcrossing hybrids are able to mature and reproduce offspring.LDH and Peroxidase isozymes of all concerned fish were determined with blood serums. The zymogram patterns of them are different.