ALLOZYME AND MITOCHONDRIAL-DNA VARIATION IN ORANGE ROUGHY, HOPLOSTETHUS-ATLANTICUS (TELEOSTEI, TRACHICHTHYIDAE) - LITTLE DIFFERENTIATION BETWEEN AUSTRALIAN AND NORTH-ATLANTIC POPULATIONS

Allozyme and mitochondrial DNA (mtDNA) genetic variation was compared in orange roughy (Hoplostethus atlanticus Collett) collected from wate rs off southern Australia and from waters about 22 000 km away in the North Atlantic west of Scotland. Samples were screened for 11 polymorp hic allozyme loci and with 9 restriction enzymes. Significant heteroge neity between the two areas was detected for three allozyme loci (ADA( ), CK* and GPI-1(*)), and the overall G(ST) (gene-diversity statistic ) value of similar to 1% was small but significant. Significant mtDNA haplotype heterogeneity was observed after chi(2)-analysis of haplotyp e frequencies but not after a G(ST) analysis. Nucleotide sequence-dive rsity analysis showed very low net divergence (0.0023%) between the tw o samples. The Australian orange roughy had a lower allozyme heterozyg osity and a lower mitochondrial DNA nucleon diversity than the North A tlantic sample. The very limited, although significant, allozyme and m itochondrial DNA heterogeneity between these areas suggests that there is some gene flow between these two populations. The species appears to be widespread, with its presence reported from the southern Pacific , southern Indian, and northern and southern Atlantic Oceans, and it i s likely that gene flow between the antipodes is mediated by stepping- stone exchange between adjacent populations rather than by direct migr ation.