POPULATION VARIATION IN THE MITOCHONDRIAL CYTOCHROME-B GENE OF THE ORANGE ROUGHY HOPLOSTETHUS-ATLANTICUS AND THE HOKI MACRURONUS-NOVAEZELANDIAE

To describe the genetic relationship among regional populations of two commercially valuable species of marine fish, the orange roughy Hoplo stethus atlanticus and the hoki Macruronus novaezelandiae, the mitocho ndrial (mt) DNA haplotypes of 59 individuals were defined by direct se quencing of the cytochrome b gene. Samples of orange roughy were colle cted on four fishing grounds around New Zealand, one off the west coas t of Tasmania and one near South Africa from 1990-1991. Samples from h oki were collected on three fishing grounds around New Zealand and one off Tasmania during the same period. An average of 252 nucleotides we re sequenced from each of 32 orange roughy and an average of 372 nucle otides from each of 27 hoki. Sequence variation allowed the definition of 9 unique orange roughy haplotypes and 5 hoki haplotypes. Genetic v ariation, as measured by both average sequence divergence and haplotyp e diversity, was high in the orange roughy (nucleotide diversity = 0.5 90%, haplotype diversity = 0.782) and low in the hoki (nucleotide dive rsity = 0.076%, haplotype diversity = 0.279) relative to a similar sur vey of the Atlantic cod, Gadus morhua. Differences in haplotype freque ncies of orange roughy from New Zealand, Tasmania and South Africa wer e not significant, and the most common haplotype was found in similar frequencies in these three geographically distant regions. Differences in haplotype frequencies between the New Zealand and Tasmanian sample s of hoki were significant, suggesting restricted gene flow between th ese two regions. The contrasting patterns of low but regionally subdiv ided genetic variation in the hoki versus high but geographically undi fferentiated genetic variation in the orange roughy may be attributed to the low fecundity, slow maturation and long lifespan of the orange roughy relative to the hoki.