Biochemical genetics and population structure of blue grenadier, Macruronus novaezelandiae (Hector) (Pisces : Merluccidae), from Australian waters

Abstract

Spatial and temporal variation in allele frequencies at 10 polymorphic loci were investigated in blue grenadier from Australian waters. Little geographic differentiation was found among three major regions. Nearly all of the detectable variation (>99%) was found within samples, while variation between samples taken at the same locality accounted for most of the remaining variation (0.8%). Blue grenadier were polymorphic at 22% of the 46 loci initially screened (P_0.99= 0.22). Overall mean heterozygosity was 0.068±0.018. This value is considerably higher than has previously been reported for this species.

Almost 700 fish were aged and typed for genetic variation. Fourteen age-classes (0+: 2-14+ years old) were compared. Little genetic difference was observed among age-classes within regions, or in the overall sample. A significant difference was found between sexes at the Est-l locus; this was due to an increase in males homozygous for the Est-l¹⁰⁴ allele in the eastern Tasmanian sample taken during August 1984. The same sample displayed a significant shift in allele frequency at the Sod locus. This sample was taken during the spawning season of blue grenadier on the west coast of Tasmania and may provide circumstantial evidence of differential spawning migration by fish with particular genotypes from eastern Tasmania to the west coast.

Comparisons of samples from Australian waters with a sample of fish from New Zealand showed significant heterogeneity at 6 of the 11 loci polymorphic in the two areas. The observed differentiation indicates that blue grenadier from New Zealand are genetically isolated from those of Australia. However, the apparent genetic homogeneity observed among the Australian samples suggests that, in the absence of indications to the contrary, blue grenadier stocks throughout south-eastern Australia can be treated for management purposes as part of a single, interbreeding unit.