Interfamilial hybridizations between female diploid spinous loach (Cobitis biwae, 2n=48) and male carp (nishikigoi, colored—carp, Cyprinus carpio) and those between diploid loach (Misgurnus anguillicaudatus, 2n=50) and male carp gave rise to inviable larval development with the expression of external abnormalities. In the colored-carp, chromosome number was about 100 and karyotype included micro chromosome and unpaired chromosome. Chromosomal observation on the interfamilial hybrids showed that they had intermediate karyotypes comprising both maternally and paternally derived chromosomes. Cold or hydrostatic pressure treatments to inhibit the second polar body release after above-mentioned hybridizations induced "allotriploidy" with two sets of maternal chromosomes and one set of paternal chromosome. Hybridizations between female tetraploid spinous loach (4n=96) and male carp and those between female tetraploid loach (4n=100) and male carp also produced "allotriploidy". Artificial inhibition of the second polar body release after these hybridizations with pressure shock produced "allopentaploidy" with four sets of spinous loach or loach chromosomes and one set of carp chromosome. External appearances of deformed larvae seemed to be improved by allopolyploidization, but no surivors were obtained.