Orange roughy from six localities around the southern coasts of Australia showed no evidence of genetic subdivision when the products of 11 polymorphic enzyme loci were analysed electrophoretically. Samples ranged in size from 84 to 171 per locality. Gene frequencies were very similar in samples taken from New Zealand. The amount of total genetic diversity attributable to subdivision among samples is estimated at 0.55 to 0.22%, but bootstrapping procedures showed that much of this diversity could arise from sampling error. A minimum of around 200 migrants per locality per generation would be sufficient to maintain the observed genetic homogeneity, although actual numbers migrating are likely to be greater than this.

A phylogenetic analysis of eight species of Pacific tunas was made after examining allozyme variation at 23 muscle and liver enzymes encoded by 35 loci. The eight species of tuna were: Thunnus alalunga, albacore; T. obesus, bigeye; T. thynnus orientalis, northern bluefin; T. maccoyii, southern bluefin; T. albacares, yellowfin; Auxis thazard, frigate; Euthynnus affiizii kawakawa; Katsuwonus pelamis, skipjack. All species except the northern bluefin were also examined for variation at three eye-specific loci. The average heterozygosity per locus ranged from 0.038 (frigate) to 0.070 (bigeye). Genetic relationships were examined on the basis of the 35 loci screened in all species. Genetic identities among the five Thunnus species were high, averaging 0.864 and ranging from 0.788 to 0.923. Whereas the albacore appeared to be the most divergent of the Thunnus species (mean identity to other Thunnus species of 0.825, range 0.788-0.452), there was little differentiation between yellowfin, southern bluefin and northern bluefin tunas (mean identity 0.905, range 0.892-0.923), and phylogenetic analyses failed to resolve the branch order among the Thunnus species. The non-Thunnus tunas were quite divergent both from one another and from Thunnus species (mean identity 0.358, range 0.280-0.606). Diagnostic allozyme loci were identified, allowing the discrimination of all species.

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Six samples (n =67 to 154) of blue-eye or deepsea trevalla were collected from south-eastern Australia (seamounts off New South Wales, a seamount south-east of Tasmania called the Cascade Plateau, off the east, south and west coasts of Tasmania, and off the coast of South Australia). All fish were analysed by starch or cellulose acetate electrophoresis for the products of seven polymorphic loci (defined in this study as those with an average heterozygosity greater than 0.06); a minimum of 24 fish per area were also analysed for 29 other less variable loci. The average heterozygosity per locus was 5.3%. Polymorphic loci showed no significant deviations from Hardy-Weinberg equilibrium. The coefficient of genetic subpopulation differentiation, GST, was 0.38%. Bootstrapping procedures showed that this low value could be attributed to sampling error alone. Contingency Χ2 analysis similarly failed to reveal any significant inter-sample differentiation for any locus. The results indicate that gene flow is sufficient to prevent any genetic differentiation among the sampled localities. During the course of the study a second trevalla species, Schedophilus labyrinthicus, was identified in the New South Wales component of the fishery.

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