Controlled breeding studies to verify the identity of roach and common bream hybrids from a natural population

The occurrence of post‐F1 generation hybrids between common bream and roach in natural populations has still to be qualified. To do this, common bream, roach, F1 and F2 hybrid progeny were produced under controlled conditions. All progeny groups exhibited overlaps in the ranges of their meristic characters. Discriminant analysis of meristic data combined with allozymes allowed identification of post‐Fl hybrids. Enzyme electrophoresis showed Fl progeny to be heterozygous at diagnostic loci. Back‐crossed F2 progeny had a mixture of homozygosity and heterozygosity at diagnostic loci. Meristic and genetic analysis of fish from a natural population indicated that they were all F1 hybrids. Post‐Fl hybridization cannot be ruled out from natural populations because Fl hybrids are known to be fertile. It is suggested that post‐Fl hybrids were not detected either because of their low incidence of occurrence or due to biological phenomenon Such as inferior fitness.