Mitochondrial 12S rRNA sequences support the existence of a third species of freshwater blackfish (Percicthyidae: Gadopsis) from south-eastern Australia

Fish of the genus <i>Gadopsis</i> are a distinctive component of the freshwater fish fauna of south-eastern Australia. <i>Gadopsis marmoratus</i> and <i>G</i>. <i>bispinosus</i> are the only two species recognised within the genus, with the former of uncertain taxonomic status, as it is thought to be composed of at least two distinct geographical forms based on morphological and allozyme data. The objective of this study was to investigate DNA sequence divergence in <i>Gadopsis</i>, especially in the western portion of its distribution, using an approximately 400 base pair fragment of the mitochondrial small subunit 12S rRNA gene region in order to reassess the taxonomy of the genus. Individuals from 11 locations were sequenced and confirm that <i>G</i>. <i>marmoratus</i> and <i>G. bispinosus</i> are genetically distinct, and further that the <i>G</i>. <i>marmoratus</i> complex consists of two divergent clades representing the previously identified northern and southern forms. The degree of divergence between the three <i>Gadopsis </i>clades was similar (5–6% nucleotide substitutions), suggesting that they diverged from a common ancestor at approximately the same period in geological time. These results are consistent with previous allozyme studies and highlight the usefulness of mitochondrial DNA data coupled with allozyme information for clarifying taxonomic boundaries in morphologically conservative aquatic organisms.<br />