Evidence for natural interspecific hybridization between the Australian bass (Macquaria novemaculeata) and estuary perch (M-colonorum)

Australian bass (Macquaria novemaculeata) and estuary perch (M. colonorum) are very similar in their morphology, use of habitat and geographical distr ibution. Following the capture from four Victorian rivers of specimens poss essing species-diagnostic attributes intermediate to the two taxa, an alloz yme electrophoresis and morphometric study was undertaken to investigate th e possibility that these individuals were the results of interspecific hybr idization. Two allozyme loci were found to be useful in species identificat ion and were used to confirm that the individuals in question were indeed i nterspecific hybrids. The presence of hybrids was further supported by univ ariate and multivariate analysis of morphological characters. Temperature-g radient gel electrophoresis on mtDNA control-region fragments demonstrated that where interspecific hybrids were identified, the maternal parent speci es was M. novemaculeata. The demonstration that M. novemaculeata and M. col onorum can hybridize in natural populations emphasizes the importance of co rrect species identification in breeding programmes to prevent the liberati on of large numbers of interspecific hybrids.