Allozyme variation and taxonomy of the river blackfish, Gadopsis marmoratus Richardson, in western Victoria

A taxonomic study of the river blackfish, Gadopsis marmoratus was conducted using allozyme and morphological data. Focussing upon populations from western Victoria and south-eastern South Australia, a total of 147 blackfish from 14 locations were scored for variation at 28 allozyme loci. The occurrence of fixed allelic differences between samples less than 50 kilometres apart suggests that G. marmoratus comprises distinct northern and southern forms, consistent with previous allozyme studies. While the degree of allozyme differentiation between the northern and southern forms is small for freshwater fish species, their recognition as distinct species is justified on the basis of the limited geographic allozyme variation within each form and the finding of a geographically abrupt genetic discontinuity in western Victoria. An examination of dorsal fin spine counts also indicated differences between northern and southern forms. However, a high degree of variation within the northern form of G. marmoratus reduces the value of this trait for diagnostic purposes, not only for distinguishing between the two genetic forms of G. marmoratus, but also between G. marmoratus and G. bispinosus.