Reproductive cycle, management and conservation of Paxyodon syrmatophorus (Bivalvia : Hyriidae) from the Tocantins River, Brazil

The reproductive cycle of a population of Paxyodon syrmatophorus (Meuschen, 1781), a mussel exploited for its shells in the lower Tocantins River, Bra zil, was studied between September 1997 and August 1998. Monthly examinatio n of gonad sections and inspection of the demibranchs of females showed tha t gametogenesis takes place all year round and that spawning occurs during the months of the dry season. Gravid females were found throughout the peri od between February and September. Sexually mature mussels as small as 23 m m in length were found and the smallest gravid female was 32 mm in length. The implications of the findings are discussed in relation to the conservat ion and management of exploited freshwater mussel populations in the region .