Effects of the herbicides clomazone, quinclorac, and metsulfuron methyl on acetylcholinesterase activity in the silver catfish ( Rhamdia quelen) (Heptapteridae)

Abstract

Fingerlings of the silver catfish ( Rhamdia quelen) were exposed to three herbicides widely used in rice culture in south Brazil: clomazone, quinclorac, and metsulfuron methyl. LC 50 was determined and acetylcholinesterase (AChE) activity was evaluated in brain and muscle tissue of fish exposed to different herbicide concentrations after 96 h (short term). The LC 50 value (nominal concentration) was 7.32 mg/L for clomazone and 395 mg/L for quinclorac, but was not obtained for metsulfuron-methyl since all fingerlings survived the highest concentration of 1200 mg/L. Brain and muscle AChE activity in unexposed fish were 17.9 and 9.08 μmol/min/g protein, respectively. Clomazone significantly inhibited AChE activity in both tissues, achieving maximal inhibition of about 83% in brain and 89% in muscle tissue. In contrast, quinclorac and metsulfuron methyl caused increases in enzyme activity in the brain (98 and 179%, respectively) and inhibitions in muscle tissue (88 and 56%, respectively). This study demonstrated short-term effects of exposure to environmentally relevant concentrations of rice field herbicides on AChE activity in brain and muscle tissue of silver catfish.