EVIDENCE OF STOCK SEPARATION IN SOUTHERN-HEMISPHERE ORANGE ROUGHY (HOPLOSTETHUS-ATLANTICUS, TRACHICHTHYIDAE) FROM RESTRICTION-ENZYME ANALYSIS OF MITOCHONDRIAL-DNA

Restriction enzyme analysis of mitochondrial DNA (mtDNA) was used to t est for genetic homogeneity of orange roughy (Hoplostethus atlanticus) in the southern hemisphere. Two hundred and eighty-six orange roughy specimens were collected from seven general localities: the Great Aust ralian Bight; South Australia (off southeastern Kangaroo Island); the west coast of Tasmania; the east coast of Tasmania; New South Wales; N ew Zealand and South Africa. Mitochondrial DNA was extracted from deve loping ovary tissue and analysed with 10 six-base enzymes and 3 four-b ase enzymes. Both forms of analysis revealed a low level of genetic di versity in this species. The six-base enzyme study found no evidence o f reproductively isolated populations of orange roughy in southeastern Australian waters. However, an analysis of 107 fish with 3 four-base enzymes identified at least partial genetic separation of the New Sout h Wales (NSW) sample of orange roughy from South Australian (off south eastern Kangaroo Island) and Tasmanian samples. This finding supports biological evidence for the presence of a distinct subpopulation of or ange roughy in NSW waters. The four-base study also provided evidence of the presence of genetically distinct samples of orange roughy occur ring in the same localities off southeastern Kangaroo Island from cons ecutive years. Additional sampling and the use of a greater number of four-base enzymes may be needed to determine if any genetic structurin g exists among orange roughy south of New South Wales.