Gonado-somatic indices and macroscopic and histological changes to gonads were monitored in an aggregate sample of 231 male and female common carp Cyprinus carpio(359–755 mm total length LT) from the River Murray in South Australia between November 2001 and October 2002. Histological inspection was most accurate and macroscopic inspection was not possible for males as discrete reproductive stages could not be distinguished. Histological photographs and descriptions are provided for each stage of ovary, testis and oocyte development. Only one (female) fish >350 mm LT was classified as immature. Spawning occurred initially over at least 7 months, from mid-November 2001 to mid-May 2002, and it began again in mid-September 2002. This is the longest duration recorded for common carp spawning in Australia. Spawning was asynchronous within the population and each female may have spawned up to three discrete batches of eggs. These data have implications for the control of common carp populations and environmental flow management in the region.