A sample consisting of 2 Ctenopharyngodon idella (grass carp) females, 2 Aristichthys nobilis (bighead carp) males, and 10 interspecific hybrids was analyzed using a multidisciplinary approach. The 10 hybrids were the only surviving specimens of a crossbreeding experiment. The cytological approach, involving the measurement of the largest axis of the erythrocytes, revealed that the parental species were diploid, whereas, among the hybrids, eight individuals were triploid, and two were diploid. Two of the triploid individuals were analyzed cytogenetically and showed 2n = 3X = 72 chromosomes. Using the biochemical and molecular approaches, it was possible to confirm that one of the C. idella specimens was the true mother of the hybrids. Those data also allowed to rule out both males from parenthood. The molecular analyses also indicated the absence of gynogenetic individuals among the hybrids. We discuss the use of a multidisciplinary approach as an efficient tool in the monitoring of aquaculture programs.

Restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) was employed to characterize species and populations of Astyanax, a Neotropical freshwater fish genus. Samples of five species, A. altiparanae, A. fasciatus, A. lacustris, A. scabripinnis paranae and A. schubarti, from the Upper Paraná and São Francisco river basins were analyzed. Two out of the ten restriction enzymes employed generated species-specific mtDNA patterns for each of the five species. MtDNA exhibited considerable polymorphism within and among populations. All populations sampled showed relatively high values of haplotype diversity. Geographically localized haplotypes were detected for A. altiparanae and A. fasciatus from the Upper Paraná and São Francisco basins. The relationships between populations are discussed.