ASSESSMENT OF GENETIC-VARIATION IN WILD POPULATIONS OF THE REDCLAW CRAYFISH (CHERAX-QUADRICARINATUS, VONMARTENS 1868) BY MEANS OF ALLOZYME AND RAPD-PCR MARKERS

The population structure of the redclaw crayfish (Cherax quadricarinat us) was investigated by analyses of allozymes and RAPD (randomly ampli fied polymorphic DNA) markers. Electrophoretic analysis of 28 enzyme l oci in 12 redclaw populations from the Northern Territory (NT) and Nor th Queensland (NQ) revealed generally low estimates of heterozygosity within each population and low estimates of genetic differentiation am ong populations except for a fixed allelic difference at the carbonic anhydrase (CA) locus between NT and NQ populations. Low levels of gen etic variability among the NQ populations is possibly a reflection of their recent radiation across the Gulf of Carpentaria after its inunda tion between 18000 and 6000 BP. RAPD analysis of seven redclaw populat ions could distinguish each river population and also grouped them acc ording to geographic proximity. RAPD analyses also revealed significan t genetic variability both within the species and within individual po pulations, which could be used to improve their culture. On a prelimin ary scale, RAPD fragments provided a useful tool for differentiating r edclaw strains and constitute a marking system that could be used in c rayfish genetic improvement programmes.