In our study, the general trend for GSI in hybrids was to be intermediate between common carp and gibel carp. In spring, the gonads of common carp and gibel carpwere highly different, suggesting some differences
in reproduction aspects. Generally, the reproduction times of both species overlap. However, there are two aspects that could explain the observed pattern of GSI and the presence of F1 hybridswith amaternal origin in gibel carp. In spring, even though the males of both gibel