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 distribution. Following the capture from four Victorian rivers of specimens possessing species-diagnostic attributes intermediate to the two taxa, an allozyme electrophoresis and morphometric study was undertaken to investigate the possibility that these individuals were the results of interspecific hybridization. Two allozyme loci were found to be useful in species identification and were used to confirm that the individuals in question were indeed interspecific hybrids. The presence of hybrids was further supported by univariate and multivariate analysis of morphological characters. Temperature-gradient gel electrophoresis on mtDNA control-region fragments demonstrated that where interspecific hybrids were identified, the maternal parent species was M. novemaculeata. The demonstration that M. novemaculeata and M. colonorum can hybridize in natural populations emphasizes the importance of correct species identification in breeding programmes to prevent the liberation of large numbers of interspecific hybrids.