Toxic effect of microcystin-LR on growth and development of a freshwater clam (Corbicula fluminea). Cyanobacterial bloom is currently one of the greatest environmental problems due to its high toxicity. However, there is little information about the toxicity of microcystin (MC) to aquatic organisms in benthic environment. This study investigated the effects of microcystin-LR (MC-LR) on the growth and development of a freshwater clam, Corbicula fluminea. The results showed that the 96h-LC50 of MC-LR for C. fluminea was estimated to be 47.0mgL(-1), and that 48h-EC50 was 3.4mgL(-1), which is about half of that reported in a recent report for a Chinese rare fish Orthocassis flavospilopterus. Meanwhile, a high content of MC-LR in C. fluminea was detected in tissue samples collected during 3days after the MC-LR exposure at 5.0mgL(-1). With continued exposure, the content of MC-LR gradually reduced in all tissues of the clam. The 96h-LC50 of MC-LR for C. fluminea was estimated to be 47.0mgL(-1). This study demonstrates that C. fluminea are highly tolerant to the toxins produced by Microcystis aeruginosa in benthic environments. However, MC-LR may induce negative effects in benthic aquatic animals if the concentration of toxins is high. This study provides information on the effects of MC-LR to organisms living in aquatic ecosystem and contributes to our understanding of the environmental impact of cyanobacterial blooms.