Abstract
Samples of Neocyttus rhomboidalis from eight areas off southern Australia and eastern New Zealand were examined to assess the stock structure of the species. No spatial heterogeneity was detected for mitochondrial DNA variation after restriction analysis by two enzymes detecting polymorphic cut sites. Twenty mtDNA haplotypes were recorded, with an overall haplotype diversity of 0·683. Twenty‐eight allozyme loci were examined; the mean heterozygosity per locus was 13·0%. Significant sample heterogeneity was detected at three of twelve polymorphic loci: MPI*, PGM‐1 * and, most strikingly (G ST =0·43), sSOD *. Most of the sSOD * differentiation was associated with depth rather than geographical separation; sSOD * allele frequencies of shallow and deep samples being very different. It is suggested that the correlation between the sSOD * allele frequencies and depth is more likely to reflect natural selection than reproductive isolation. The spatial patterning of the MPI * and PGM‐1 * data suggest there are at least three geographic stocks of N. rhomboidalis in Australasian waters: (1) New Zealand, (2) Western Australia and South Australia, (3) west Tasmania to New South Wales and Lord Howe Rise.