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 waters off southern Australia and from waters about 22 000 km away in the North Atlantic west of Scotland. Samples were screened for 11 polymorphic allozyme loci and with 9 restriction enzymes. Significant heterogeneity 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 haplotype frequencies but not after a G(ST) analysis. Nucleotide sequence-diversity analysis showed very low net divergence (0.0023%) between the two samples. The Australian orange roughy had a lower allozyme heterozygosity and a lower mitochondrial DNA nucleon diversity than the North Atlantic sample. The very limited, although significant, allozyme and mitochondrial 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 is likely that gene flow between the antipodes is mediated by stepping-stone exchange between adjacent populations rather than by direct migration.